My favorite tribe: Wizards. Not very supported one in general, but here’s one:
Naban, Dean of Iteration
1U
Legendary Creature — Human Wizard
2/1
If a Wizard entering the battlefield under your control causes a triggered ability of a permanent you control to trigger, that ability triggers an additional time.
The problem here is that the whole thing pretty much writes itself. I mean, there’s pretty much the right number of useful blue wizards with ETB-abilities available, so not much to do here.
Hmm… Not really enough… (and I’m using a couple of cards I wouldn’t normally use, because they are quite expensive).
Well, Dominaria has the following:
Academy Journeymage
4U
Creature — Human Wizard
3/2
This spell costs 1 less to cast if you control a Wizard.
When Academy Journeymage enters the battlefield, return target creature an opponent controls to its owner’s hand.
Merfolk Trickster
UU
Creature — Merfolk Wizard
2/2
Flash
When Merfolk Trickster enters the battlefield, tap target creature an opponent controls. It loses all abilities until end of turn.
Naru Meha, Master Wizard
2UU
Legendary Creature — Human Wizard
3/3
Flash
When Naru Meha, Master Wizard enters the battlefield, copy target instant or sorcery spell you control. You may choose new targets for the copy.
Other Wizards you control get +1/+1.
That gives us 21 Wizards. I guess that means we should have Azami as well.
Well, we do want to get more of those triggers as well, if we don’t have that many creatures.
After that, I guess I have to fill the deck with spells. We do have some synergies with instants and sorceries, so let’s move on from there. First, we need some basic card draw. I like to start with ones that cost three to cast, because you want ones that can smooth out your land drops. You can expect to hit three mana fairly consistently.
That should help a little. Also, these are good if you draw them later on as well, so that’s a plus. I’ll put in a few other draw spells as well.
Some more would be nice, but we have plenty of value from out wizards, so we won’t need too many of these big draw effects.
Also, counters and some mass bounce, as blue often does:
… and that makes 61 cards, meaning we have room for 38 lands. Is that enough? Not sure. I feel like there’s enough small creatures to be enough, so I’d go with that.