Flexible Waterbender

The Waterbend mechanic runs on tapping your board to pay a cost, and here it buys a full inversion: a 2/5 wall that flips into a 5/2 attacker for the turn. That defensive stat line is the resting state, the shape you keep between combats; the waterbend activation is the swing you cash in when you have the mana and the tapped bodies to feed it. Vigilance is the piece that ties the two halves together, since it lets the creature attack in its 5/2 form without surrendering the block it would otherwise offer at 2/5. The waterbend cost itself is deceptively soft: the base is steep, but every artifact and creature you tap knocks a generic off the bill, so the activation gets cheaper the wider your board gets. That makes it a payoff that scales with clutter rather than with mana alone, rewarding a go-wide shell that has spare bodies sitting idle after their own attacks or triggers resolve. The design tension is the usual convertible-blocker problem: a card that wants to hold the ground and a card that wants to close a game, resolved by letting you choose which one it is each turn rather than committing at deckbuilding time.