The commander
Yidris, Maelstrom Wielder: A piece that enhances all other strategies but isn't needed to win. Can be used as a counter- or removal magnet to push through another line. One one hand, isn't too good in creature heavy metas because it is hard to trigger him. On the other hand, the big body can block a lot of creatures and is sometimes large enough to survive small boardwipes. In rare cases the stats are high enough to finish people with combat damage.
Instants
Abrupt Decay: This spell can hit almost anything because of the low average manacosts in cEDH decks, you'll have to play around the few cards this can't hit. The fact that it can't be countered makes it incredibly good since counterspells are quite common. A few fringe counterspells work against decay because they don't explicitly counter the spell.
Ad Nauseam: One of the best cards in the deck since the high starting life total and low average cmc ensures you can draw a lot of cards. The card comes with a deckbuilding restriction. The best moment to play this is usually in the end step before your turn. That way you have the most mana available during your own turn. The deck is also capable of winning off of a main phase cast, but isn't built around it. Usually you try to win after having cast the card but there are situations, such as being in a slow game or being really unlucky with what you reveal without the direct need to win, where you can cast the card for value.
Assassin's Trophy: A good cheap spell that can remove anything. Most people play at least a few basic lands because of cards like this. Giving your opponents a land is an upside for them, so try to keep this card in hand as long as possible. It can also be used as a soft wincon if you are able to loop through your deck in some way.
Brainstorm: If you have access to a shuffle effect then this usually feels like a 1 mana draw 3. In other cases it gives you specific cards at an earlier moment. During cascade turns you can also put cards you want to cascade into back on top of your library, making it especially good with the suspend spells.
Chain of Vapor: Often used to bounce back all your own fast mana to go mana-positive. Because you have to sacrifice most or all of your lands, this should only be done when you're almost sure you can win that turn. This also turns off cards that synergize with your lands such as High Tide and Frantic Search. As an interaction spell, this card has the downside that people can also bounce one of your own permanents. If you really need to interact with someone winning the game, it's advantageous to bounce another player's permanent, so they are forced to sacrifice a land to deal with the actual problem. They can also bounce the problem back to you, so only do this if their target is of really high value.
Dark Ritual: Black is the deck's second most important colour and this is one of the most efficient rituals in the game. A lot of our payoff cards also need multiple black mana.
Demonic Consultation: A piece of the core combo. Often used to exile your library by naming a card not in your deck. Can also be used as a tutor in urgent situations, but using it as a tutor is not recommended. If you play it too early then you risk exiling cards you need to win, but by waiting too long you increase the chance that the named card is in the top six. If you know what one of the bottom cards in your deck is then it's usually better to name that card and not exile your entire library.
Dispel: A narrow answer Comparable to Red Elemental Blast. The most important cards both can hit are Flash and opposing counterspells. This card can also hit Ad Nauseam, Assassin's Trophy, Demonic Consultation, Tainted Pact, Vampiric Tutor, Pyroblast, Veil of Summer and Silence.
Dramatic Reversal: This card is used as a ritual that often produces 4 or more mana. It can also combo with certain cards, most notably Isochron Scepter, Bonus Round and Narset's Reversal. Can also be used to synergize with Deathrite Shaman, especially if you can keep recasting it.
Drown in the Loch: A flexible card that acts both as a counterspell and as removal. Two mana counterspells are not too amazing, though. The most important part is the flexibility. Against some decks, such as Yisan and sometimes Najeela, you cannot hit the commanders with the removal fast enough.
Flusterstorm: A narrow counterspell, but one that is hard to interact with because each copy is a spell itself. Mainly used for protecting your own combo.
Force of Will: A staple in most blue decks because it's a 'free' spell, even though exiling a card from your hand is a real cost. The one life usually doesn't matter that much. You need to run at least around 30 blue cards to make this worth it, so it comes with a deckbuilding restriction. Since the cost of casting it for 'free' is pretty high, use it only in critical scenarios. The fact that it is 5 mana also makes Ad Nauseam slightly weaker.
Frantic Search: A free spell with three cmc, which makes is very good for hitting higher costed cascade targets. This provides card selection, but also card disadvantage. It synergizes with cards that make your lands tap for more than one mana, such as High Tide and Utopia Sprawl.
High Tide: Blue is the most important colour, so the deck runs a lot of islands. This makes this card often a blue Dark Ritual. It becomes even better when you also have cards that untap your lands.
Impulse: Instant speed card selection that lets you look at four cards. Pretty good mostly because it's instant speed, but not the most efficient draw spell overall.
Mana Drain: Both an interaction spell and a colourless ritual, depending on the scenario. Being two mana makes it harder to protect your own combo with, since you are often really tight on mana during the combo turn. The fact that it can counter anything while also doubling up as a ritual, even though you don't need much colourless, is what puts this card over the top.
Manamorphose: This spell is completely free, both returning you a card as well as the mana. The only downside is that you don't know what you're going to draw, and thus don't always know what colours to name. If the spell is copied or reduced in cost, it even gains you mana.
Mental Misstep: Most played counterspells are one mana, making this spell very good at protecting your combo at no mana cost. Also very good at countering your opponents relevant early spells when they're faster than you.
Mystical Tutor: A few of the most important cards in the deck are instants or sorceries: Tainted Pact, Demonic Consultation, Ad Nauseam, Wheel of Fortune and Windfall. This is almost always used to find one of these cards and continue with your game plan. It going to the top of your library can be a small downside, but depending on what you want to find, also an upside if you can cascade into that spell. It can also find you a lot of other cards, since most of the deck is instant and sorcery based.
Noxious Revival: Free spells are incredibly good, especially so In Yidris when they still have a mana cost of one or higher. This spell is practically a tutor that only looks at your graveyard, most often being used to return a Jace or oracle when they both end up in the grave. In cascade turns, you can put relevant spells, often suspend spells, back on top of your library to cascade into. It can even be used to stop opponents combos if they need to use a specific spell in the graveyard, such as Worldgorger Dragon decks.
Opt: A filler card to find the cards you need. This being instant speed makes it so you can hold up interaction, but it doesn't dig much. Not a bard card to include, but not a great card either.
Pyroblast: There is very often a blue deck at the table, but even if there isn't this spell can target non-blue permanent due to the specific wording. It won't destroy non-blue permanents though. The reason this card is doubly good is because it isn't dead when cascaded into, while the other counterspells often are.
Red Elemental Blast: A second copy of Pyroblast with the downside that this can't be cast on anything that isn't blue, making it less good to cascade into or when building up storm. It's comparable to Dispel and mostly used against enemy counterspells and Flash. Cards this can hit that Dispel cannot hit are Jace, Wielder of Mysteries, Thassa's Oracle, Mystic Remora, Rhystic Study, Timetwister, Gilded Drake, Notion Thief and Narset, Parter of Veils.
Repeal: Most often used to return a mana rock back to your hand to draw a free card, but can also be used as interaction when needed, even though this is slightly expensive. Even just bouncing an opponent's Chrome Mox or Mox Diamond hurts.
Snap: A good tempo play against creature based decks. It synergizes well with High Tide. Since it doesn't draw cards or permanently get rid of a creature, it's also nothing more than a tempo play most of the time, but the fact that it can act as a small ritual is what makes it better.
Swan Song: One mana counterspells are very good, but often restrictive. So is this one, but it often hits important targets such as opposing counterspells. Keep in mind it only hits enchantments, and not artifacts. Also try to not give a bird to your opponents too early, unless needed, since that is going to likely cost you quite some life over the course of the game. It's often best to keep it to protect your own combo.
Tainted Pact: One of the most important cards in consultation, as it can be used to both find your wincon as well as exile your library. It's often correct to choose one of the bottom few cards of your library if that helps you protect your win, rather than just shortcutting to exile the rest of your library. It is also a good instant speed tutor that has you lose access to certain lines. Make sure you don't exile both wincons. In the storm variant this card is also pretty good, but you have to be even more aware of what lines you lose access to by exiling too much. You can be pretty liberal with exiling your deck in the consultation variant to find a specific card.
Vampiric Tutor: One mana tutors are very good, especially when they are instants. The two life is more than worth this card, since it represents the best current card in your deck. It loses some effectiveness in the later game when you need to threaten a win that turn, since you also need a way to draw a card.
Veil of Summer: A good protection piece that protects your cards for the rest of the turn. Incredibly good if your meta has a lot of counterspells, but not as spectacular if you often have to use it as a one mana drawspell. It does only give protection from blue and black to cards that are on the battlefield when it resolved, so keep in mind people can still target permanents you play later that turn.
Sorceries
Demonic Tutor: For two mana you can get the most important card in your deck. If you don't specifically plan to cast what you are searching this turn or the next, then it's likely better to keep it in your hand, see what else you will draw, and then decide what to tutor for. An exception to this rule is finding counterspells early to protect your combo later.
Gamble: One mana tutors are good, especially when they go into your hand. This one is slightly risky because you have the chance that you discard what you tutored for. It might be unsafe to use gamble to find one of your wincons if it's the only one in your deck and you have no other ways of getting it back any more.
Gitaxian Probe: Free spells that draw cards are good, especially because this also triggers cascade. The information this gives can be used to see if you can safely try to win that turn or whether it's good to wait. it's almost always correct to pay 2 life rather than the mana.
Imperial Seal: One mana tutors are good, but this being a sorcery doesn't let you hold up interaction as well in most cases. Still, it's an incredibly good card, but not one that you can't do without for budget reasons.
Infernal Tutor: A spell that can find a wheel or other payoff spell when you've used up every card in your hand. It also synergizes with Lion's Eye Diamond, but you should be pretty certain your opponents do not have interaction. Since the deck doesn't run any duplicates because of Tainted Pact this card does literally nothing if you cannot get rid of your other cards, but otherwise it's a second copy of Demonic Tutor.
Mind's Desire: Seems like a costly card, but this usually provides you with a lot of card advantage and even mana advantage after just a few spells. Cascade turns usually double up all your spellcasts. When you run cards that can return the spell to your hand it's better to let the original not resolve before you have looked at all the free cards provided by the copies. Even in the worst case scenario, where it exiles a lot of lands, you will not draw these lands in following turns. In the storm variant, this spell can be used to make looping more consistent by letting unwanted cards stay in exile.
Ponder: Great card selection that lets you look at four cards, either the top three or the random card on top of your library after shuffling. Great for finding specific cards you need.
Preordain: Another great card selection spell for just one mana, possibly digging a total of three cards deep. Scrying is a little less relevant with the amount of shuffling the deck does, so cards hardly stay on the bottom of your library for long, but at least you will not draw those cards now.
Regrowth: Not so good in the early turns, but can be used to get a specific spell out of your graveyard that you need later in the game, for example wheel effects that were already used. Also relevant to get back one of your win conditions, since the deck only contains two. Don't hesitate returning a fetchland if you need to hit your landdrops. In the storm variant this can be used in infinite loops.
Wheel of Fortune: This card becomes progressively worse later in the game since it often refills your opponents hands just as much. It's good to quickly cast a lot of spells, then follow it up with a wheel. If played incredibly early, it can even disrupt your opponents hands. In the storm variant, it's better to tutor for this card than Timetwister in almost all cases, to fuel Yawgmoth's Will or simply to keep twister safe from graveyard hate for loops.
Windfall: Another wheel effect, also generally gets worse later in the game. Overall, Wheel of Fortune is often stronger, but sometimes an opponent has drawn a lot of cards and has more than seven in his hand, in which case windfall will draw you even more cards. Drawing four to six cards for three mana is still an incredibly good ratio, but be careful not to refill you opponents hands too much as well.
Yawgmoth's Will: Over the course of a game a lot of spells will end up in your graveyard, this spell enables you to replay them all. Don't feel bad for casting this card early just to get value out of it, you don't always need to win the game after resolving it. Remember that this card exiles itself because of its own effect. In the storm variant, casting this card makes it so you are unable to win using loops that turn.
Artifacts
Arcane Signet: Signets and talismans are already pretty good, and this doesn't cost you life or require additional mana, as well as tapping for all relevant colours by itself. The best signet or talisman in the deck.
Chrome Mox: Exiling a card from your hand is a real cost, especially in the storm variant. But being able to cast something a whole turn earlier usually rewards you more, especially if it's a large payoff card as described in the 'how to play' section. Don't exile cards that you assume you will need to win that game. Exiling a red or green card is usually not that good, since you don't need much of that colour.
Dimir Signet: The deck needs a certain density of ramp cards as well as artifacts. The signets are generally better because they can tap for mana instantly, but blue and black are so important that a signet isn't bad. Costing generic mana is also pretty good during cascade turns, since there are a few effects that only provide colourless mana.
Fellwar Stone: You opponents usually play enough colours to make this the second best signet or talisman in the deck. It can be tapped without further mana or life investment.
Lion's Eye Diamond: A card that gives quite some mana, but can only be used together with specific spells such as tutors and wheels. It also combos with Wheel of Fortune and Underworld Breach, making you draw your deck until someone draws interaction. It's also a free spell to build up storm or to trigger cards like Song of Creation. Very good when these cards come together, but the card is unplayable without any setup as it cannot be used as a regular mana rock. This makes it one of the worse cards to cascade into. Even if you have a card that synergizes with it, you will still have to discard your hand which makes you weak against counterspells. It can also easily turn on metalcraft.
Lotus Bloom: A decent card to suspend on turn one or two, in later turns I would rather keep it in my hand to put back on top of my library in some way unless you know the game is going to go longer. One of the best targets to hit during cascade turns, it's a Black Lotus then.
Lotus Petal: Being able to cast spells a turn earlier is incredibly good. Sometimes it's better to keep on the field to turn on your Mox Opal, but otherwise don't be afraid of using it, even on something like a talisman.
Mana Crypt: The deck doesn't have that much generic costs, but ramping yourself by two for 0 cost is amazing. This could mean turn 1 wheels, or early "free" talismans.
Mox Diamond: The deck doesn't run that many lands, so it can sometimes be hard to fulfill this condition. If the choice is between playing the land or the diamond, it's often better to just play the land, unless you can abuse the fact that it's an artifact, for example by untapping it or to attain metalcraft. Because of this card it's usually correct to hold up one land during cascade turns. If you cascade into it and expect to have a land later than turn, then don't cast it yet. You are likely to cascade into it later that turn.
Mox Opal: This artifact comes with a deckbuilding restriction, namely needing to play enough artifacts to consistently have two others in play. Because of this, it's often correct to remove the opal if you play less than 15 artifacts. In Yidris this amount can be around 13, as your cascade turns practically guarantee hitting enough artifacts.
Sol Ring: The deck does't need a lot of colourless mana, but getting one mana instantly and then two every following turn is incredibly good. It also doesn't have any real downsides. There should be a very good reason to not include this in your deck.
Talisman of Dominance / Talisman of Curiosity / Talisman of Creativity: The talismans are slightly stronger than signets because you don't need an additional mana to activate them, while the lifeloss isn't usually that much. It is going to stack up over the course of a game though, making you draw less cards with Ad Nauseam and Necropotence. In some cases you can also use them to tap for colourless, but the deck is quite colour intensive so this hardly happens. All talismans are blue focused since that is by far the most important colour in the deck.
Creatures
Arbor Elf: With 11 relevant lands in the deck (duals, shocks and fetches) there are usually enough land that enable this card. Sometimes you can fail in finding a forest, which makes this card do absolutely nothing. Tapping for blue is rather important in the deck though.
Birds of Paradise: Can tap for any colour while only casting one, one of the best mana dorks in the deck.
Deathrite Shaman: One of the other best mana dorks in the deck. While it can fail to produce mana if there are no lands in graveyards, the other abilities provide you with an alternative win condition as well as some life. It can also stop certain combos that rely on the graveyard. There being no lands in graveyards hardly ever happens with the amount of fetches players run, and there's almost no downside to exiling your own fetchlands aside from cards like Regrowth and Yawgmoth's Will. In the storm variant this can be used as a consistent back-up wincon because of loops.
Dockside Extortionist: This card is often better than most rituals we have, and can make a lot of mana in a turn. I like to compare it to Cabal Ritual which costs two and adds five. This card is slightly worse than cabal if it makes less than 5 mana, but even then it has the upside of adding mana in different combinations of colours as well as not needing threshold, and you can use it the next turn(s) as well. The artifacts also help attain metalcraft for Mox Opal. Having two toughness also makes it able to block mana dorks to deny Tymna triggers. If this card often makes three treasures or less I would consider cutting it.
Elves of Deep Shadow: Black in the second-most important colour in the deck, so this is a good inclusion. Losing 1 life every time you use it does decrease the effectiveness of a few other cards, and makes it harder to use in the infinite mana-untaps combo.
Notion Thief: Combos with the wheels played in the deck, making you draw all the cards and your opponents none. Also very good as an instant speed interaction piece when other players are generally drawing a lot of cards. The card is easy to counter or remove, so don't go all in on this card if you can avoid it.
Thassa's Oracle: The most logical comparison is Laboratory Maniac. The upside of this card is that you do not need a draw effect, and can win without removing your whole library. It also costs a mana less. This card also does something for you when setting up, although you will need a way to replay it later. It can also block a lot of relevant creatures. It is worse against Torpor Orb style cards and Stifle effects. It also is harder to play out early in a turn to set up for a win, so this is something you will have to play around.
Enchantments
Carpet of Flowers: A card that does nothing against non-blue decks, but in most cases there will be a blue deck at the table. This can easily give you two or three mana each turn, as well as choose the colour of mana you need. This is stronger than most of the one-shot rituals in the deck.
Counterbalance: Most people see this card as a set-up counterspell, which it isn't. It is an incredible tempo piece because most cEDH decks run cards around the same mana cost. It's comparable to a Chalice of the Void for 0, 1 or 2 that only hits your opponents. In some cases, for example using topdeck tutors, you can even guarantee countering certain spells when necessary.
Mystic Remora: One of the best cards in cEDH decks, practically an auto-include in every deck that can run it. Either people decide to 'not feed the fish', severely hampering their options. Or you draw a lot of cards for a low mana investment. It's usually right to stop paying for the upkeep once you see you have more impactful cards already in your hand.
Necropotence: Really food in refilling your hand, but more importantly finding the specific cards you need to win the game. I don't recommend using this to refill your hand every turn, as losing your draw step is going to cost you a lot of cards over a longer game. There's no hard rule on how much life to pay. Often it's better to see what kinds of cards you still need, how many cards are in your deck and estimate how many cards you would need to dig to find all needed cards. Do remember that you permanently lose access to everything exceeding seven. The discard-to-exile is a trigger you can respond to, if you really need to save something. In the storm variant of the deck, this card is less good as you need a high density of cards and discarding to exile is going to shut off certain winning lines.
Rhystic Study: More of a stax effect, good players know to pay . If your meta hardly pays, then this is a fantastic include to draw you a lot of cards over the course of a game. It doesn't do anything during the combo turn, and three mana is also a bit high to just play it for storm count.
Song of Creation: A very risky piece to play since you have to discard your hand at end of turn. But what is storm if not risky? Many other comparable cards that have this effect are way more mana or only draw you one card, even with stricter requirements for the types of spells you cast. This card giving two cards per spell makes it incredibly likely to go off if you can cast a lot of mana-positive spells, especially because other cards in the deck also let you dig deeper. The fact that you can also play an additional land helps you start the chain. If you have absolutely nothing else in hand you could try to play this early, discard your hand and hope you can go off with whatever nonland you'll hopefully draw the next turn, otherwise I can suggest keeping this card until you're ready for a win attempt. When also cascading with Yidris you draw cards for both the original spell as well as the spell you cascade into, and the draw is not optional, so make sure not to deck yourself.
Underworld Breach: Comparable to Yawgmoth's Will in that it lets you recast cards from your graveyard, but this exiles other cards rather than the played card. This makes it incredibly good to remove your deck with. The most common examples would be using a card to exile your library and then casting a wincon from your deck as often as needed and as mana and cards allow. Using High Tide and Frantic Search also allows you to gain mana by recasting the latter a lot of times, turning one card in your graveyard into three mana. It also dumps two of the three cards you need to exile in your graveyard already, and the mana can likely partially be used to cast draw spells. Wheel effects are also incredibly good with any of the mana positive spells in the deck, since they refill your graveyard to cast even more spells. Eventually, this ensures you can empty your library to win. Also don't be afraid to just play this card for value when needed.
Utopia Sprawl: Comparable downsides to Arbor Elf as you need a forest in play to effectively use it. The upside is that it doesn't get hit by creature removal or cards that shut activated abilities down. Also synergizes well with cards that untap your lands. Compared to a dork, this also gives you your mana back immediately if you have at least two untapped lands.
Planeswalkers
Jace, Wielder of Mysteries: The secondary wincon of the deck, since Thassa's Oracle costs two mana less. It's often not correct to play this card for value, as you have almost no way of protecting a planeswalker. The biggest upside of Jace is that the draw effect and win effect are on the same card. He does cost a lot of blue mana though, which is something to be prepared for. As Jace's effect is a replacement effect, cards like Notion Thief or Narset, Parter of Veils will not work against Jace with an empty library. Since you're the affected player, you can choose if you want your opponent to draw a card or if you want to win the game.
Lands
Arid Mesa / Bloodstained Mire / Flooded Strand / Marsh Flats / Misty Rainforest / Polluted Delta / Scalding Tarn / Verdant Catacombs / Windswept Heath / Wooded Foothills: Fetchlands can slightly thin your deck, which might increase your win percentages by a small margin. Practically, this will only be relevant when playing hundreds of even thousands of games. The main reason why these are good is because they can find you your dual and shock lands, which ensures you can hit the right colours when needed.
Tropical Island / Underground Sea / Volcanic Island / Bayou / Badlands: The very best lands that tap for more than one colour. They enter untapped, have basic land types and don't have additional costs. The only downside these have is that they don't tap for all four colours and that they are nonbasics, and sometimes get hated out.
Breeding Pool / Steam Vents / Watery Grave: These have basic land types, meaning they can get fetched and enter untapped when needed at the small cost of 2 life.
Morphic Pool: A land that taps for the primary colours that practically always enters untapped.
Island / Snow-Covered Island: There are a few cards that hate on nonbasic lands, so the deck still runs some basics so that is able to interact with decks that play these cards. There are also a few spells that let you look for basic lands, most notably Assassin's Trophy. Island are also important for High Tide.
City of Brass: A land that taps for all colours that only deals one damage to you, great for getting the right colours at the right time. The damage is a triggered ability, so you can win or gain life in response to the trigger to not die.
Command Tower: The best all-colour land in this specific format, having no downsides except getting hit by nonbasic land hate.
Exotic Orchard: With the efficient manabases each cEDH deck has, this land also often taps for all colours. The downside is that this doesn't tap for anything if you play first and play this as your land.
Forbidden Orchard: This card is a little worse than the ones that deal damage to you, since you have very little ways to deal with the creatures, often causing you to take more damage in the long run. You need a lot of lands that can tap for all colours. This card does provide other players with blockers for Tymna the Weaver, which denies your opponents resources.
Gemstone Caverns: If this land is in your opening hand and you're not playing first then you're effectively ramping yourself at the cost of a card. It's also a land that taps for all colours. Tapping for colourless is a real downside in other cases.
Mana Confluence: A mana of any colour for one life is a good ratio. This is a cost rather than a trigger, so you can not respond to it. It can also not be prevented.
Taiga: Blue and black are the main colours of the deck, so a card that taps for the two secondary colours is not that relevant. It's still one of the more efficient lands in general, but is hardly ever fetched.
