Ouroboroid

The trick with a snowball engine is who gets to hold the snow, and this one hands it to the whole board. A 1/3 body is a slow start, but the counter distribution scales off its own power, so the loop compounds: every combat step, the wurm feeds itself X counters along with everyone else, and X is larger next turn precisely because of what happened this turn. Cast it in the precombat main phase and it fires that same turn, so there is no dead cycle to wait through: the engine starts the moment it resolves ahead of your first combat. Left alone for a couple of turns the numbers get absurd, because the anthem is quadratic rather than additive: a wide board multiplies the payoff, and the payoff then widens each creature further. Because the trigger keys off the beginning of combat rather than an enters trigger or an attack requirement, the counters land before blocks are declared and before any creature has to commit, rewarding a full board that simply exists in front of you. The 1/3 print keeps the whole thing fair: it enters as a modest body that only matters once you already have creatures for it to pump, and a board wipe the turn before it swings erases the plan. The engine asks you to already be ahead on creatures, then punishes an opponent who cannot answer the wurm before that lead turns lethal.