When you have a toolbox, knowing your tools as well as what tools to use when is critical to success. In Scion we effectively have a dragon-based toolbox, and knowing what tool to use when is often the difference between and unsatisfying loss and an epic win. As such, I'll do my best here to explain how each of our dragons our used. I'll divide them into categories so that readers know what to prioritize.
Critical Tier 1 Dragons
These are the dragons that are the most critical to the deck's success, which you really don't want to leave home without. They play different roles, but each is a critical part to winning, and you'll see these most games.
1) Karrthus, Tyrant of Jund
If there is one dragon most critical to your success besides Scion himself it's this one. The difference between playing this deck before and after I got Karrthus is pretty dramatic. The first ability is very niche, but the ability to give all our dragons haste is of unparalleled importance. It's far less good if we mass reanimate our dragons only to give all of our opponents a full round to kill and board wipe them. It is far better to just swing in and kill one or all of them. He's less critical if we already have another haste spell on the board, but often enough we won't, and Karrthus is the haste enabler we can tutor which our opponents often won't see coming. I wouldn't leave home without him.
2) Teneb, the Harvester
This is both a Dragon tribal and a reanimator deck, and as with the above, we'll often have other spells to reanimate with, but this one is always on tap to be tutored up at instant speed. There are few things better than tutoring The Ur-Dragon on Scion and hitting with him the one turn, only to reanimate The Ur-Dragon and Bladewing the Risen permanently the next turn. Teneb makes these things possible. It's always comforting to have him in the 99, ready to be called to service at any moment as needed.
3) Bladewing the Risen
Have I mentioned this card enough yet? It's because he's just that good, and basically gives us a free, hand-picked dragon every time we cast or reanimate him. There's really not much more to say, other than that you'll play him every game and love it every time.
4) Silumgar, the Drifting Death
While we have other dragons which can help Scion protect himself, this one is the simplest and usually the best. For two mana Silumgar will give Scion hexproof, which will cause your opponents' spells to fizzle and their tears to flow. It's a bonus that when reanimated, he causes each of your dragons to give a -1/-1 debuff to your opponents' creatures on attack, creating a hidden board-wipe that gets around indestructible and other such annoying effects. Silumgar is definitely the cream of the crop.
Guardian Dragons
Instead of guardian angels in this deck we have guardian dragons! These are dragons that protect Scion when we make him a copy of them. While Silumgar, the Drifting Death is chief among these, there are others that are relevant as well.
1) Quicksilver Dragon
This is the card that will really make your opponents think twice about pointing removal at Scion. You just need to remember to have a single blue mana open in addition to the two you pay to make Scion a copy of him. Then you simply redirect that spell at the best thing of the person who targeted you (or something else on the board if there is something scarier, but that has less pedagogical value). Once you've done this enough, your playgroup will be jumpy about trying to remove Scion when you have mana open!
2) Skithiryx, the Blight Dragon
The flashiest thing about Skittles is his infect ability, but that is the least of this card's abilities. It's great when it works and you can get an infect kill, but it takes a lot of setup. Skittles is best for simply using his ability to regenerate Scion for in the event of a board wipe or a targeted destroy spell. Board wipes are less ubiquitous in commander these days, but among those that destroy creatures, regeneration will dodge the majority, and this is a great ability to have on tap. In addition to this his one mana ability to grant him haste can also help us get Scion swinging a bit early. While I played this deck without him successfully for many years, Skittles adds lots of utility to the deck that is always appreciated.
3) Kairi, the Swirling Sky
This card can both protect us from targeted removal while also providing upside in a board-wipe if you we can't save Scion. Ward is fantastic protection from targeted removal as your opponents won't often be willing or able to pay for it, and as such I'd use this piece before Silumgar if they are unable to pay the tax. In addition, both of the "dies" triggers are great here. Milling a bunch of cards and then returning instants or sorceries (especially reanimation spells) to our hand will speed our recovery. If there aren't good targets for this, getting revenge by bouncing a bunch of non-land permanents is great way to hose an opponent's ramp package or otherwise discourage them from messing with you in the future.
Disruptive Dragons
These are dragons that we can use to interact with our opponent's board to deal with problematic permanents and board states. Despite being in five colors we aren't playing lots of silver-bullet removal cards like card:Sword to Plowshares and such. If we did, we'd water down our dragon-based toolbox and slow down the deck, so we settle for sorcery-speed, Scion-based removal pieces instead. Usually we're the aggressor anyway, so we can afford to be less controlling. Each of these pieces are important to know because they play an important role in helping us overcome key opponents and win. It's also worth mentioning that these effect are repeatable turn after turn if we reanimate them from the yard.
1) Vaevictis Asmadi, the Dire
I'm surprised more dragon decks aren't playing this gem, because he's the best removal piece there is. When we attack with him each player must sacrifice a permanent of our choosing. This means hexproof, indestructible, you name it we can destroy it. This is because we are not technically targeting anything, even though we get the privilege of selecting what we want them to give up. Yes, we have to sacrifice something too, but to trade a land or a mana rock we no longer need for each opponent's best thing is an amazing deal. Don't sleep on this one, it's as premium of a removal card as you can get.
2) Tyrant's Familiar
This card is great because when we attack with it, we get to do seven damage to any creature, which is enough to kill the overwhelming majority of creatures in the format. There's nothing about it, this is removal stapled to a dragon. This card also is great because it gives us haste so that we can use Scion the turn we cast him, and he gives Scion +2/+2 to boot. He's also low enough cmc that we can hard cast him when we want to, which just makes this a great card all around.
3) Balefire Dragon
This is a board wipe targeting only one player which we can activate with Scion. This is great because we're aggressive and don't always have good blockers up, and that pesky token player might be gold-fishing and threatening to overwhelm us. We'll teach him good by bombing his whole section of the battlefield with dragonfire. It's death from above, as they say.
4) Steel Hellkite
This is the most absolute board wipe attached to a creature we've got, and in many cases is the ultimate solution to our woes. We just need to make Scion a copy of him, then attack and do damage. After that we pay x and all non-land permanents with cmc less that x are consigned to the dust heap. As with most cards, I remember well a game I won where this saved me. My opponent was running a populate deck and had an artifact based recursion engine which allowed him to keep copying an exiled Angel of Sanctions, which he then could populate to keep my stuff locked down. In the meantime, to tokens had haste, and he was chipping away at my life total. I had destroyed the tokens a few times but he could keep making more with his artifacts and some other pieces of his engine. Steel Hellkite got the job done. I was able to destroy all the pieces of his engine, along with other mana rocks and enablers to boot. Having cleared the obstruction, the game ended swiftly afterwards. Also, as an extra, this card also has the ability to pay mana to pump it to a larger size, which is always helpful when going for infect or commander damage wins. This is a solid card.
Utility Dragons
These are the dragons that grease the wheels and keep things moving smoothly for us. They don't win games on their own, but they often set us up to win.
1) Savage Ventmaw
Ramp and card draw wins games, as they say, so why not use Scion to give us a ton of green and red mana that doesn't leave our mana pool? This card is of especially good value if we play it early, as we can pay the two mana activation, attack with Scion, and have plenty of resources to set up our support pieces while still having some left for our opponents' turns. If we can recur it later, we'll have more mana than we know what to do with!
2) Dragon Mage
Ramp and card draw wins games, as they say, so why not use Scion to discard our hand once it is low (perhaps dumping some good dragons in the yard for later reanimation) and draw seven fresh cards. It is hard to state how good it is just to have this on tap for when our hand is low and need a refill. In another deck we'd have to hope to top-deck such a spell, but our commander gives us guaranteed access to it for two mana of any color. It's nice to have a commander that is also a tutor.
3) Old Gnawbone
Getting ramp in a dragon deck is great, and treasure is very on theme also. This dragon can immediately get us seven treasure tokens as a Scion target, which is a great value on its own, and if we get her onto the battlefield she will hoard us this value every turn. This card is a fabulous addition to the deck!
Pump it Up!
These are cards that help all of our dragons get bigger and do more damage, whether temporarily or permanently. It might seem like dragons deal enough damage on their own, but we get hate in this deck and we want to power up as much as possible.
1) Dromoka, the Eternal
Weirdly enough in the early days of playing this deck I wasn't super excited about this card, but my experience has taught me better. This card is just an engine that bolsters your whole team every turn. It gets out of control really quickly. It is also fairly easy to hard cast, which is a plus as well.
2) Kolaghan, the Storm's Fury
This one is a temporary effect, but a killer one nonetheless. When each attacking dragon adds up to an anthem that all attacking creatures get till the end of the turn, the game will be over quick, especially if one of those dragons is Atarka, World Render.
3) Spellbound Dragon
This is another dragon that I wasn't excited about at first and thought about cutting, until it helped me snatch victory from the jaws of defeat. The problem with many of our other pump activated abilities on other dragons is that we won't have enough of the right mana to power them. This simply lets us discard a card and pumps Scion (when it is a copy of spellbound) by the cmc, which is often a large number. This definitely helped me achieve a commander damage kill in a game when I wouldn't have been able to afford to otherwise. It's also useful just to loot sometimes when we need a card, especially when we can often just reanimate the discarded card later.
4) Moltensteel Dragon
We've mentioned this before in the win cons section, but as with Spellbound Dragon sometimes we need to resource other than mana to get enough damage for the kill, so how about using our life as a resource? This dragon has definitely finished out games for me and is not one to forget about.
Getting the Job Done
We are finally into our powerhouse dragons that finish the game!
1) Utvara Hellkite
We can go deep or we can go wide with our dragons (and sometimes both!), and this card follows the go wide strategy. Utvara gives us no less than a 6/6 dragon token for each of our attacking creatures. This fairly quickly can double our board presence and win games on its own. When you begin to think about the synergy with other things that care about numbers of dragons such as Scourge of Valkas your mins might explode. One key thing to know about using it though is that even if we have a haste enabler out, we still won't be able to attack with the tokens until our next combat. This is because in magic attackers are considered to be declared at the same time even if on-attack triggers use the stack, so once the tokens are created attackers will have been declared, and as such we won't be able to attack with them immediately. This is why the next card on our list can be so helpful.
2) Lathliss, Dragon Queen
Like Utvara Hellkite, Lathliss can get us dragon tokens, making her very powerful. Unlike Hellkite who gets these triggers on attack, Lathliss gets them on ETB, which makes her a worse Scion target but a far better mass reanimation target. If reanimated along with a few other dragons we will effectively double those extra dragons, and as we can do this before our attack step we can attack with them the same turn if we have a haste enabler on the battlefield. This is better than Utvara in that Utvara's tokens are created when attackers are declared, and as such cannot be declared as attackers themselves.
3) Scourge of the Throne
Sometimes one combat isn't quite enough to kill everyone, so why not two? This is especially good when Utvara Hellkite is in play, but it is always good. We only have to make sure that we don't have the most life, something Moltensteel Dragon can help us with if we need it and he's out.
4) Atarka, World Render
The only thing more powerful than doubles trike is a brood of double-striking dragons. Usually when I play this I win that turn, or the game is at least over in practice. It's that good. It might be tempted to play this early, but hold off until the time is ripe and you won't be disappointed!
5) The Ur-Dragon
It's ironic but perhaps fitting that I put Scion's namesake last since it is often the first dragon I copy each game. I'm confident I play The Ur-Dragon far more than those who have him as the commander, because I can get him out for two mana. Nonetheless he goes in the finisher category because he is great both early and late in the game. It's great to remove a quarter of someone's life total and half the commander damage they are allowed to take from you early in the game, while also putting any permanent we want onto the battlefield and drawing a card. It's then great to use a second or even third time later in the game when it can have even more impact, drawing more cards, having more permanents you can cheat in, and doing tons of damage, especially if pumped by Atarka, World Render or other effects. I play Scion because I respect The Ur-Dragon too much to have him functioning as a glorified Urza's Incubator from the command zone. Free The Ur-Dragon by playing Scion of the Ur-Dragon! I rest my case.