Wakka, Devoted Guardian

Combat-damage triggers usually reward you for connecting once; this one snowballs the whole board off a single hit. The artifact destruction is a rider you can decline (destroy "up to one"), which keeps it live against opponents with nothing worth blowing up, but the +1/+1 counter it drops on itself is not optional, and that counter is the fuse for the real payoff. Because Blitzball Captain checks only whether a counter landed this turn, any source will do: the combat trigger, a proliferate effect, an anthem counter you placed on your own turn. Once that condition is met, the end-step trigger fans a +1/+1 counter out to every other creature you control, which turns a wide green-white board into a threat that grows faster than opponents can trade into it. Reach and trample are connective tissue rather than decoration: trample makes the combat trigger hard to fizzle behind chump blockers, so the counter that feeds the end-step reliably arrives. The design sits in the go-wide-with-counters lineage green-white has circled for years, but it collapses two jobs a deck normally splits between an aggressive body and a counter-distribution engine into one four-mana creature. That collapse is the whole appeal: it wants to attack immediately, and every successful attack makes the next turn's board bigger, so the clock and the value engine share the same card.