Pollywog Prodigy

The design trick here is that one ability quietly rewrites the other's fine print. Evolve grows the Frog off your own creatures, and every counter you land pushes up the power number that gates the draw trigger, which fires whenever an opponent casts a noncreature spell cheaper than that power. Fresh off the board at 1 power, it already reads the free stuff: mana-value-zero artifacts and spells all cost less than one, so a Mishra's Bauble or a Lotus Petal cracks the draw before you have grown at all. Push power to 4 or 5 and the window widens to catch most cheap removal, cantrips, and interaction the table can muster, punishing the exact play patterns blue wants to punish (a wall of one- and two-mana answers) without asking you to hold up a counterspell yourself. The catch is that the 1/3 body only reads what opponents cast, never your own spells, and it wants to survive long enough for the counters to stack. It sits in a small lineage of blue creatures that convert opposing spellcasting into cards, but where most of those keyed off a fixed cost line printed in stone, this one hands the pilot the dial and lets the ceiling climb over a game. Get it clear of cheap removal and the reward compounds precisely as the threat grows hardest to answer: the bigger it gets, the more your opponents pay you for the privilege of interacting.