Sprite Dragon

The clearest distillation of Izzet's core tension: a creature whose entire value proposition is contingent on the spells you would rather be casting anyway. The body starts as a 1/1, which means it does nothing until the deck does what it already wants to do, and then it grows on every noncreature spell, cantrip, burn, or counter alike. That contingency is what keeps the rate honest: it rewards the spell-density build without taxing it, but it punishes a slow draw mercilessly, dying to anything if you stumble on lands or run dry. The lineage here is Monastery Swiftspear, which proved that haste plus a growth trigger keyed to noncreature spells could anchor a tempo deck; Sprite Dragon carries that template into two colors and trades raw early aggression for evasion. Flying is the structural upgrade that makes the second color worth it: every counter lands on a body most opponents will struggle to block, so the prowess-style growth converts directly into unanswered damage rather than getting chump-blocked away. What you get is a creature that scales with its own deck's velocity and asks nothing more of you than to keep casting the spells you brought.