This is the standard Dragons deck. i might make edits later on or not. we'll see.
The goal of the deck is to win. obviously. but how? Many decks can have various ways of "winning". sure most of them involve putting the opponents life to 0, but getting there has many routes. most peoples commanders are representative of what that deck is trying to do. So lets get into the habit of reading a commander and figuring out what the deck is supposed to do. The Ur-Dragon is a big chungus of a card. 5 color with plenty of change. but he has an eminence ability. Eminence is special in that it means that it's possible to get value out of the commander without ever playing them. so one way you could read this card is that the player is using it soley for it's eminence ability and never plans on playing them. the other idea is that they do plan on playing them. if we think about it though, if they are playing cards that they want to reduce the cost, that usually means the cards that they are playing are relatively high cmc on their own. and the deck is likely built to be able to pay those costs if it has to. so even if the deck doesn't plan on casting ur-dragon, it probably can.
looking at the rest of Ur-Dragon we can see he rewards tribal, allows for big expensive cards to be easier and encourages combat. so from there if we are sitting across from the deck we should assume that the cards our opponents play will probably be one of those things or some supporting card to that idea.
Well that was good practice. but The Ur-Dragon is our commander. we don't need to guess whats in the deck we need to build it/ understand the list. as the resident big chungus, ur-dragon supports hitting people over the head with big bois. When trying to understand a deck there are many ways to analyze cards, but broadly speaking we will want to look to answer a few questions. "How does this card help further my goals?", "When is this useful?", and "What does it cost to play this card?". Certain types of cards will tend to answer these questions the same way so as we go forward i will introduce terms for these types of cards as we discover them and explain how to use these groupings to our advantage.
First lets explore the questions. starting with "How does this card further my goals?". All cards should further our goals otherwise we shouldn't play them in our deck. some cards also are better at furthering our goal than others which we will also consider in this question. For certain decks like combo this could be as simple as "Getting this card out is the goal!" others might be a bit harder to explain and change depending on the deck. for example Wall of Omens is a pretty good card but why it's good and how good it is depends on what your deck does. for slow decks like control/combo this card is good because it helps keep your hand full of responses as well as providing blockers on the ground to keep you alive into the late game where you likely want to get to. however in a deck that plays cards like Flickerwisp and Panharmonicon it's important to state that it has an "enters the battlefield" ability (abbreviated ETB) that the deck plans on capitalizing. in this deck though, the fact that it replaces itself is ok, but you don't care about putting a small wall on the ground to block. and it doesn't matter that the ability is an etb vs some other type of trigger so you it doesn't further your goal very well.
next question, "When is this card useful?". Not all cards are useful at all times. some cards are sort of useful at some times but are way more useful at other times. a big part of understanding why this question is important is understanding how often the situations it's useful in come up. another way to understand the question and how others will also refer to this is "how often is this card useful?". lets look at an example Damnation. this is a board wipe. it's use is very clear, use it when you want to empty the board. so lets talk about when we want to do that. it would be easy to say "when the board is full" but thats not quite right. we wouldn't want to blow up the board if we have more creatures than anyone else and no one has anything scary. so a better answer would be "when it's more important to get rid of our opponents creatures than to protect our own". this is a little broad and probably could be broken out into several smaller answers such as "I have no creatures and opponents do", or "my opponent has game winning creatures out, and i prefer not to lose". okay now lets see are there any situations that it's more or less useful than normal? well if you opponent only has 1 creature then this card while technically a way to kill that creature, is likely no longer worth it. and obviously we discussed that this card is amazing if everyone but you has a massive board. now for the hard part, how often these scenarios happen. this depends on who you play with and what decks you plan on going against. against slivers i expect them to put together a large board fairly often.
lastly "what does it cost to play this card". mana usually obviously but what else. almost every card has the bare minimum cost of a slot in your deck. by playing this card, you are not playing a different card so it has to be better than other similar cards. other cards have very clear costs such as Dangerous Wager. but others are a little bit subtler such as Dusk. dusk has costs. to get the most value out of a card like this, you'd want to play less cards with 3 or more power and more cards below.
Now that we have the questions out of the way, lets talk about the cards in the base list for the deck. why they are in here and what cards we would take out and why.
The Ur-Dragon: This is the commander and baseline of the deck. they are always useful due to eminence, they further your goal of playing lots of dragons to beat down your opponents with by making it easier to cast and because they sit in the command zone and not in your deck there is little to no cost to having this card around.
Atarka, World Render: if goal is to hit people to death with dragons this effectively doubles the effectiveness of all other dragons. This effect is powerful enough that it should help close out most games it's allowed to swing in. this is useful when you have other dragons out but is still alright by itself meaning it should be fine in most situations you can play it. but due to mana cost that wont be for a little bit.
Bladewing the Risen: there is a concept called the vanilla test, which is checking to see how a cards power and toughness line up with it's mana cost. a card is said to pass the vanilla test if it meets or beats its CMC with it's power and toughness before considering it's abilities. so a 2 mana 2/2 passes. a 1 mana 2/1 passes. and a 3 mana 3/4 all pass. the pass or fail on it's own isn't a reason to put a card in your deck but it can help give an idea of how good a cards other features need to be in order for the card to be good. a card that fails the vanilla test needs a better effect than a card that passes the test in order to be equally as good. a 4/4 for 7 fails the vanilla test pretty miserably which means you need some pretty stellar effects to make it worth it. flying is good but sort of the baseline for what we would expect. resurrecting a card is a powerful ability and so is the pump. both of these things really help move our game plan along. this card is pretty poor early on in developing your board as the card needs to be able to get value out of the first ability, but much better in the later stages of the game. this card does require dragon tribal but that's already a given for your deck so this isn't a very bad cost and i will probably stop bringing up this cost on future cards.
Boneyard Scourge: with the addition of flying most would argue that this passes the vanilla test. bonus fact if a creature's only abilities are keywords such as trample, haste or flying a card is often referred to as 'french vanilla'. a flying dragon with a reasonable power will be useful to our game plan, and the ability to help us recover after losing creatures is great for stabilizing our board presence. This card is great early as it can be an aggressive beater, but even more so because even if you lose it in some risky attacks, theres plenty of time to recover it. only cost here is tribal support.
Broodmate Dragon: 2 4/4 flyers for 6 mana. a sorta 8/8 for 6 passes the vanilla test. having flying dragons does help the beat down plan, but 2 4/4 isn't game winning, it's just alright. 4/4 flyers with no other abilities would be great in the early game to out race other smaller flyers and get some early beats in, but 6 mana doesn't really cut it. there is a concept called 'the curve' in magic. the basic idea is that for most decks you want more cards with lower costs and you gradually have less and less of cards as you go up in mana costs. if you have a bunch of 8 mana cards in hand, you'll likely have to wait a long time to play them and even when you do get to, you'll only be able to play one a turn. so the cost for this card is that it takes up one of your 6 drop spots which are inherently more competitive due to the scarcity of the spots. This is a card that i would argue is closer to the chopping block. though this card is much better when paired with cards that care about quantity over quality such as Utvara Hellkite which we will discuss later.
Crosis, the Purger: 6 mana 6/6 with flying passes vanilla. (shortening to V+ and V- for future cards because i don't want to keep typing it). it's ability can also remove cards from opponents. now since hitting people to death is our goal, it may seem like the ability doesn't further the plan. however since most of your opponents will usually want to play cards to stop you, removing those cards stops being from stopping you. so it does have the ability to further the game plan. in order to use this card's ability you either need to have nothing else you'd rather want to play, or have enough mana to use the ability after casting your other cards. in terms of cost, we are mostly looking at opportunity cost. using the ability means not developing your board usually. also this effect is likely to draw the ire of other players at the table.
Deathbringer Regent: V- destroying all creatures includes your own which can be pretty bad for our game plan. this card is very useful for evening a lopsided board, which is a good thing. However the effect is not optional, so if you're board is good you just can't play this card. the timing of when to play this card is so important that i would say that the cost of playing this card is that your 7 drop spot is a card you can't play in half of scenarios. personally i'd cut this card.
Dragonlord's Servant: ~V, but that's not as important because this card isn't really looking to hit people. it's here to help get big things out faster which is great for the plan. its useful in all but the late game when you have enough mana that the cost reduction isn't important. as it's a low drop which you want more of, the cost of playing this card is pretty low.
Dragonspeaker Shaman: V-, basically more efficiency Dragonlord's Servant. having multiple of the same effect is great for something called 'consistency'. ideally you want to win. winning usually requires you to do somewhat similar things each game. so having the ability to replicate those scenarios by having more opportunities to get your important effects is great. very low cost to play, though more than a two drop.
Dromoka, the Eternal: V+, flying beater that makes things bigger. exactly what we want for the plan. at 5 mana this card will likely come out at a good spot on the curve. it's effect can trigger on a 4 drop attacking that you might have cast the turn before playing it. the cost of this card is actually a little strange. the cost is that you don't want to play low toughness creatures that you don't want to attack with. because the lowest toughness cards get the buff having cards like Dragonlord's Servant out means that you'll need to attack multiple times before your dragons are the ones that get the buff.
Hellkite Charger: V-, attacking is the goal. getting a second attack in a turn is very amazing. most of the time using this ability should kill someone. however this card isn't exactly an army by itself. so it wants to be played as at the end in order to close out a game. this type of card is called a 'finisher'. some cards can work as finishers and also in other scenarios such as Atarka, World Render. most decks want at least 1 or 2 good finishers but you don't want to overload the deck with them as most of the time.
Intet, the Dreamer: V, this card is very similar to another card we looked at. Crosis, the Purger. so we can do a shortcut and just look at the differences between the cards. intet helps build up our board and will likely cause much less hostility at the table. i'd prefer this card over crosis.
Kolaghan, the Storm's Fury: V-, but when it attacks it becomes at least V. this card gets much better the more dragons you have out, is ok by itself but not great. another plus is that it has optional haste which allows us to close out games with a surprising damage boost that people don't see coming. probably not a finisher because most of the time it won't be enough to take out the whole table and is much less surprising after the first swing. at 5 mana it's also lower on the curve making it's cost to include smaller.
Niv-Mizzet, Dracogenius: V-, draw power to get more dragons is good. hitting people is free cards which would be great. using the ability to draw when the board is cluttered is also acceptable. meaning this card is useful in most situations. the cost is that the card costs two sets of double colors. not always an easy task in a 5 color deck, you may need to devote resources to color fixing to play this and use its' ability consistently.
Ojutai, Soul of Winter: V-, the card slows opponent's down which can be good for the plan. it could prevent blocks but the goal is to have big enough things in the air that blocks don't matter. it is a 7 drop which means it's going to be a while before you can resolve it.
O-Kagachi, Vengeful Kami: V+, the effect is nice if someone else is being aggressive back at you, but most of the time if someone is aggressive at you, it's usually because you are not in a state to fight back. so the 'when' of this card is much less frequent. WBURG is big ask and a serious cost to consider.
Orator of Ojutai: ~V, 0/4 does not help plan. replacing itself is helpful but you'd rather it just be a different card you'd actually want. early cut card.
Ramos, Dragon Engine: V-, but quickly becomes V+ after even a single cast. big beat sticks are always on plan. the possibility of using it's other ability to have a sudden burst of mana and build a board out of no where is also great. timing wise you want it before other multicolored dragons but if it has to come after it's not the end of the world. as a colorless card that gets powered up from basically everything in your deck there is very little cost.
Ryusei, the Falling Star: V-, it's abilities don't help progress the plan but act as insurance against removal. it's death likely will take most of the ground based board with it which shouldn't affect you. the cost here is playing very few ground based creatures.
Savage Ventmaw: V-, 4/4 is a small body for you. extra mana is very nice though with all the big creatures. but it requires that you already have 6 mana which means you had enough to cast most creatures already. could help get two creatures out in a turn but not as often as you'd like. cost is that you want to be playing more green and red cards to be able to get value out of it's ability.
Scalelord Reckoner: V-, sort of protection against removal is very helpful. great to land before other creatures so that they don't respond to it's cast with their removal spell but it's likely that so long as you have a few creatures out that playing it after isn't a problem either. double white is the cost.
Scion of the Ur-Dragon: V, the card is heavily dependent on what else is in your deck, but because you likely have other cards in the deck that further the plan this card usually does as well. because this card can copy other cards that are useful at various points in the game, this card is useful at all points. the cost her is mostly on you as a player. you will want to keep in mind what cards are good to grab with this. you don't need an encyclopedic knowledge of your deck. probably just know the top 5 cards you'd want to grab with this card and when you get them out, just think which of the 5 would be most useful. a tip for figuring out which cards are better than other, the copied creature never enters so it doesn't ever trigger deathbringer reagent but you can use the ability before you attack so you can get the abilities of Atarka, World Render.
Scourge of Valkas: V- and could make itself V+ but its usually too expensive to do so. playing dragons hurts people a lot is really good for the plan. you'll preferably want to play this earlier but it coming down late still provides some value. triple red is a big ask.
Silumgar, the Drifting Death: ~V, killing opposing creatures that could stop you, is good for the plan. hexproof and a lot of toughness makes it hard to get rid of. many people play 1 toughness creatures so this card is still good even if it's the only dragon.
Spellbound Dragon: V-, but likely V+ when attacking. you often want to play big dragons. so getting rid of them for a power boost doesn't usually end well. great synergy with bone scourge though.
Steel Hellkite: V-, but can make itself V+. pumping a creature to hit someone hard is great for the plan. note that X can be zero if you want to blow up tokens. usually a solid plan. being colorless and able to have a built in response to most sized creatures make this have little to no cost.
Sunscorch Regent: V-, gaining life to stay alive longer is kinda part of the plan but not really. earlier is better since in the late game fewer cards are cast. double white is a cost.
Taigam, Ojutai Master: V-, not being countered is helpful but doesn't actually further the plan. you want to play it earlier when you still have cards in hand to cast afterwards as it's very poor with nothing else coming after it. you want plenty of instants and sorceries in the deck to make use of the ability.
Teneb, the Harvester: V, compare against Crosis, the Purger. more creatures mean more damage means helping plan. building self is less hate inducing than hurting others. 3 mana is also usually cheaper than casting creatures yourself. so long as someone has a creature in grave this card is great. similar cost to Intet, the Dreamer.
Territorial Hellkite: V+, fast high power is great for plan. but drops off in usefulness as the game progresses when swinging wildly into someone likely will get the creature killed without any benefit. double colored.
Tyrant's Familiar: V- into V. fast and big with bonus damage to eliminate threats/blockers. good stuff but mostly only if you have your commander out. (great choice to hit with scion if scion is your commander). cost is mostly that it's a 7 drop that is fairly underwhelming for how high up on the curve it is.
Utvara Hellkite: V-, MOAR DRAGUNS. probably the definition of a finisher. playing this card and attacking with the rest of your field is almost certainly a game over unless dealt with immediately. costs be damned this card is great to get out.
Wasitora, Nekoru Queen: V, casual removal that sometimes give you more flying beaters is helpful to plan. though the card is far less useful if the enemy has multiple expendable creatures. 3 specific colors can be tricky, but the fact that the opponents field is so important to this card's effectiveness means that the real cost is mostly in consistency.
Cultivate: Getting more mana helps you cast dragons sooner, meaning earlier beat downs. good for plan. decent early game, less so later. only hits basics, so if you don't have many you might not end up being able to grab the type you want to.
Crux of Fate: wiping only opponents cards is pretty great as it removes threats and blockers. pretty good at most times. not much cost, just hope the enemy doesn't have any dragons.
Earthquake: used to wipe non-flyer pests from the board. this won't eliminate blockers usually as your creatures all have flying. x likely won't be high enough to be efficient to hurt enemies directly. so this only helps the game plan if the enemy has creatures on the ground that would pose serious threats to the plan. in which case it's probably a worse crux of fate. but most things will be.
Farseek: helps fix mana and ramp. note that it doesn't say basic, so you can grab shock lands like Blood Crypt.
Fortunate Few: this one is risky as you will have some of the scarier threats on board and most people won't let you keep anything good. so you might get hurt more than others which is bad for the plan unless the opponents had a pretty substantial lead on board.
Fractured Identity: this card is just fun. removing a threat only to give it to everyone else is usually bad though giving yourself a copy of a card that can help close in for the kill is possible.
Kodama's Reach: see Cultivate
Painful Truths: in your deck this should be a 3 mana draw 3, lose 3 life. 3 life is fairly insignificant, especially in commander. always go for 3. refilling the hand with more dragons when you are low is great for the plan, but how often are you low on cards in hand? lots of dragon decks can get their hand clogged with high cmc cards and having a few extra in hand doesn't solve the issue. so this card while good usually has the cost that you probably need to make sure the rest of your deck is streamlined to take advantage of this.
Rain of Thorns: Destroys multiple cards of various types that all can help your opponents or even hurt you. seems fairly reasonable for the plan. but at 6 mana it's likely your entire turn. the 6 mana isn't a bad price for all of these effects, but for the card to be worth the mana you need to want to use all 3 effects. that includes the land destruction part. how often do you usually want to destroy a land?
Armillary Sphere: getting lands to hand can help fix colors and make sure you don't miss land drops. however this is only helpful to the plan if you weren't going to hit your color/drops. this is useful early but not late. cost requires multiple basics in deck.
Commander's Sphere: provides mana which can be useful for the plan. useful early, later game when it's less useful it can replace itself. no cost.
Darksteel Ingot: mana is helpful for the plan. not being removed easily can prevent others from preventing this aspect of the plan, but unless an opponent is going to try and destroy this, and you have no other target for them to destroy this part isn't as important. cost is not playing a different mana producing artifact (often referred to as a rock) in this slot.
Dreamstone Hedron: produces more mana, even more plan. ramp is always useful earlier rather than later. hedron timing was has issues in that at 4 it can be a little later than you might otherwise want a mana rock coming down. but it also does have the benefit of being able to be sacced for value if you do draw it later after you have enough mana.
Fist of Suns: this card is similar to a rock in that it can help get cards out earlier which is great for the plan, but it scales in effectiveness depending on how expensive the cards you are trying to get out are. a 5 cmc card is no cheaper, a 6 cmc card is 1 cheaper, but a 9 mana card is 4 cheaper. this effect is multiplied if you cast multiple cards. the cost of this card is actually that to take advantage of it you'll need to have lots of high cost cards.
Herald's Horn: cost reducers are close to ramp so they help the plan. comes out earlier than Fist of Suns but also doesn't scale up with the cost of cards in the same way. but in exchange it also gives possible card advantage. as with anything related to getting things out quicker, this card is much better early than late. cost wise, recognize that opponents will get some knowledge of dragons that are about to come out. revealing a powerhouse like Atarka, World Render or Utvara Hellkite means opponents will likely hold back any removal they were planning on using so that they can save it for your threat.
Lightning Greaves: protect your finishers and make sure most of your creatures get to come in with haste seems pretty good for the plan. the only condition for this card being good is that you have creatures, which sometimes you might not have either due to all of them being to expensive to cast or you don't have any more in hand after a wipe. shroud means you can't target them either. this prevents cards like Temur Battle Rage or other spells that help your creatures (often referred to as 'buff spells'. spells that specifically give power or toughness boosts are more specifically called 'pump spells').
Mirror of the Forebears: having a second copy of a big flying dragon for a huge discount sounds very on plan. this card much like grieves needs creatures to be useful.
Nihil Spellbomb: many decks have lots of cards that provide value from the grave. this card can stop them which if it stops enemies from being effective at stopping you is good by the plan. but the 'when' in when is this card useful is much more dependent on who you are playing. there are certain decks where this card will single handedly shut off their entire strategy albeit temporarily. other times this card will do nothing, but thankfully it has a way to replace itself in those situations so it's not completely useless.
Sol Ring: best mana rock you'd be willing to pay for. twice as good as most mana rocks at a major discount. it's not great at the end of the game but the potential power boost early is very enticing.
Wayfarer's Bauble: similar to Cultivate but you get to break up the spent mana over 2 turns if you need to. in exchange you don't get the extra land to hand.
Crucible of Fire: making dragons bigger is on plan. when is this useful? well obviously when you have dragons, but you are not playing Giant Growth so what's the difference. crucible is a permanent effect that applies likely to your whole board so there is that. but there are several cards that can provide a buff to a single creature at a much cheaper cost. the reason for crucible is that it buffs multiple creatures and that even if they remove a creature with something like Doom Blade you didn't lose out on any extra value. so you need to make sure to take advantage of this card you have lots of dragons out as this card is not very beneficial to a single dragon. however is does get better when paired with cards like Atarka, World Render which multiply the effectiveness of the power boost.
Curse of Bounty: Curse cards are detrimental effects to put on another player. the commander specific ones such as this one are specific to attacking and also provide a boost to you and the attacking player instead of causing a direct problem for the cursed target. this one in particular untaps things for you. this can be used to give your creatures psudo vigilance so long as you attack the cursed target which is fairly good for the plan, but if thats the goal you will be providing many of your enemies a strong benefit that you won't be able to capitalize on. this card also untaps your rocks which can help you cast multiple things in the same turn, but unless you have a way to capitalize on it untapping on your opponents turn you will run into the same problem as before. so the cost of this card is that you want to include cards with tap effects or instants to use on other peoples turns.
Curse of Opulence: compare to Curse of Bounty. this card can be dropped as early as the first turn and provides mana to help accelerate your curve and get angry dragons out earlier which is very good. like any form of acceleration this card is better early rather than late. This card is different than bounty in that you don't need to play any other types of cards to capitalize on other players attacking the target. but not every deck will be willing to attack early meaning that this card likely won't be triggered unless others desperately need the 1 extra mana.
Curse of Verbosity: better to compare to Curse of Opulence than Curse of Bounty. more people would be willing to swing in order to get a card draw but this card is actually better later than early. card draw is most effective when you don't already have the card you want (note wanting anything or just more cards is still wanting a card). in the early game you are mostly just looking to play what you have, and with the number of high costed cards in a dragon deck you likely won't need more cards for at least a little bit. but in the late game people are more willing to throw out attacks and you will have the mana to actually use all of the extra cards you will be drawing instead of just discarding to 7 each turn.
Dragon Tempest: Dragons having haste and bonus damage is good for the plan. obviously in order to take advantage of the haste and ETB triggers, you'll want this card out earlier. note that this does work with any non-dragon flyers that you might be playing as support. this card like Crucible of Fire benefits from lots of ok creatures as opposed to a small number quality creatures.
Elemental Bond: drawing more dragons is great for the plan. very comparable to Dragon Tempest but you get card advantage (some way of improving your ability to play cards, such as drawing more of them, getting higher quality cards through effects like scrying. this could also count as putting cards like Faithless Looting into the graveyard where it essentially is still in your hand due to flashback) instead of damage.
Frontier Siege: options for you are always a plus. options for opponents are always a minus. this card helps ramp which is good for the plan or it could help remove opposing threats which are both good for the plan. at 4 mana to get 2 mana ramp this is similar to Hedron Archive, however there are some differences. the mana is colored and you get it twice a turn making it like 4 mana per turn. but you can't choose when to use it, which means you don't get to use it on cards like Scion of the Ur-Dragon mid-combat. on the fight, so long as you play big creature, you get to remove a small creature whenever you play a creature. the cost is that this card works best with big strong creatures as opposed to multiple small creatures.
Kindred Discovery: more dragons in hand to play is good for the plan. as stated before, card advantage is most useful when you need cards. when you are at a point where you are playing and swinging with dragons you will likely be at a point where you want to get more cards, so the timing tends to work out. this card works best with multiple smaller creatures as opposed to a small number of big creatures.
Monastery Siege: options. first option, card advantage in the form of filtering what cards you want in hand. an effect that is equally useful throughout the game. option 2, protecting your expensive cards from cheap removal is nice, but will likely only slow opponents as opposed to stop them. if you have a threat, they will answer it. this just says that they have to spend their full turn doing so instead of just half a turn.
Palace Siege: options. card advantage through recursion (the term for bringing things back from the graveyard). this card is useful later in the game after you've had several cards die, though at 5 mana this is cheaper than a lot of dragons. the other option of enemies losing 2hp and gaining 2hp is fairly lackluster as 2 damage per turn is fairly small compared to the 6 damage you can do with good sized dragon. so it takes quite a bit of time for the 2 damage to rack up to a point where it's relevant.
Your land base is extremely important in a 5 color deck. however i do not feel like reviewing like 34 cards that all come down to "Land, you need these. mountains produce red. make sure you have enough of these."