Shoal Serpent

A wall that forgets it's a wall, but only on the turn you feed it land. The body is a real one: a 5/5 trades up against most of what its era put across the table, and defender is the single clause holding the price down. Defender never stops it from blocking, so it always works as a backstop; what the keyword denies is the attack step. The landfall trigger buys that back, and only that, expiring when the turn does. The design idea is to bolt an offensive threat onto the one resource every deck spends anyway, so the question is never whether you can power it up but whether your land sequencing lines up with the turn you mean to attack. The wrinkle is sharper than it looks. Because the freed-up state wears off before your next turn arrives, a fetch land cracked on an opponent's turn does nothing for your offense: to swing, you put the land down on your own main phase, before combat. And since the serpent has no haste, its first turn on the battlefield is a wasted attack regardless of land drops; summoning sickness keeps it home. So this is a defensive fixture first, parked as a hard-to-kill blocker, then activated later by sequencing a land into the precombat main phase of the turn you finally want it to come off the wall and hit.