Well, plenty of problems here…
First, instead of the usual one promo rare for each pack, there’s a selection of eight from which you get one. So, you can’t really predict what you’ll get, which is good for the sake of the game, if not the usefulness of this article.
Second, its a wedge world, meaning each of the packs will be based on three colors, which in turn means that mana is going to be horrendous despite the uncommon fetch lands, common lifelands, and the common banners. The banners will put a lot of pressure on your three drops, possibly screwing your curve badly… and that’s just if you’re lucky enough to get them.
Even without such complicated manabases, an even higher percentage of sealed games are decided based on manaproblems than usual. In this set, where you often need three color, you’ll be screwed even more often. There will be situations where you draw your nice triple land, but its the only source for two of your colors. It’ll be awkward, since you can’t cast your bombs with it. During four or five rounds of play, this will happen quite a few times.
As much as possible, try to avoid pure three colored decks, unless you have a really strong manabase. Otherwise, you should basically be two-colored, splashing a couple of cards. It will help your mana immensely.
Abzan’s clan ability is Outlast, which is basically putting +1/+1 counters on the creature with a tap and a mana cost. The problem is that it only works sorcery speed (and otherwise it would be way too powerful). Still, its a good ability on its own, especially in sealed, where games often get clogged down by way too many creatures on both sides of the battlefield. Outlast gives you a way to build your forces while waiting. Sure, it will be slow, but its something.
Also, many of your creatures will give bonuses to creatures if they have +1/+1 counters. This will give you sort of reach in the game, where time will be your friend. You’ll probably often find yourself being the control player, because Temur and Mardu are just so much faster out of the gate, but if you can hold on for long enough, you’ll probably be able to pull a win.
Jeskai’s ability is Prowess, which gives the creature +1/+1 until end of turn whenever you cast a noncreatures spell. Combat will be nightmare for your opponents, because every instant you have is turned into a combat trick, often turning them into two for ones. On the other hand, the clans don’t have many spells, mostly just creatures. You should probably use things like instant speed card draw to give you bonuses.
Its important to find a good balance between creatures and spells. You’ll probably want more spells than usual in a sealed deck, but you’ll still need to draw the creatures. Gladly, we have some experience with this from Theros limited with all the heroic creatures, but it will still be pretty hard.
I’ve heard Sultai is pretty popular, but I don’t really know why. Its clearly the control clan, and playing control can be quite awkward in sealed. Also, they seem to have many moving pieces in the cards, and getting the right mix will be difficult.
Their clan mechanic is Delve, which is familiar to us from a couple of cards from Future Sight. What it does is that you can pay part of your spells (colored mana only) by exiling cards from your graveyard. You should take trades when possible (but be wary of Jeskai trickery) to give you more resources. You can build and use your graveyard in other ways too. It all just requires more planning then usual.
Mardu is the fastest and most aggressive of the clans. Their ability is Raid, which simply means that if you play a creature with a Raid ability, and you have attacked on the turn, the ability triggers. The abilities are quite varied, including a creature that can return to the battlefield from the graveyard if you attacked on the turn, to a creature that will take four of your life if you haven’t attacked, to a creature that will shock (do two damage to a creature or player) when it comes to play.
The ability means that sometimes you will need to chump attack with a small creature to trigger the ability. Of course, you can bluff a trick this way. There will be situations, where you can take advantage of a situation if you actually have a trick and your thinks its a chump attack, or doesn’t block and you play a Raid creature, which makes him think you didn’t actually have anything.
Temur is base-Green, which means that their real special ability is that they have the cheapest creatures. Green is generally very strong in sealed, where the size matters most, and removal is limited. Their clan ability is Ferocious. Like Raid, it isn’t really an ability, but more like a collection of similar effects they gave a common name to because players like that. Ferocious means that something happens or something happens differently if you control a creature with power four or more.
Temur does have its share of tricks, because it is part blue.
It would be a good idea to familiarize yourself with some of the more common morph-cards in the set. There’s plenty of them and many of them have good abilities. You’ll see plenty of them during the day. You probably can’t play around all of them, especially since you can’t really memorize all of them. Just remember [scryfall]Ruthless Ripper[/scryfall].
You should note that the set has been designed in such a way that all the morph creatures with morph cost less then five are either pretty fragile or they have very low power.
Play Temur. I won’t though. I chose Sultai, because it has the most cards I want for my EDH collection. Still, green often has the advantage just for being big, and Temur has the best handle on that from the three green clans. However, more than usual, I’d say just follow your instinct. What’s the style of deck you most like to play? Go with that.
Also, there was a sort of pre-prerelease on Sunday at the Community Cup. You can learn much from that. You’ll find it on WotC’s Twitch channel in its entirety.