Bronzebeak Moa

The body is the trigger's only weakness: a 2/2 that taxes nothing, so the +3/+3 it banks each time another creature joins it has to outrun the fact that it dies to almost any removal in response. The reward is genuinely linear in a go-wide shell. The turn after it lands, chain a pair of cheap creatures and it swings as a 5/5 or an 8/8, each entry stacking another temporary boost until end of turn. That makes it a payoff for token generation and flicker effects, where the count of creatures hitting the battlefield matters more than the quality of any one of them: a single board-refilling spell can spike it into lethal range mid-combat, since the trigger fires on each entry, not on a one-time cast. The design tension is that the buff is fleeting and conditional on a board you have to commit to first, so a clean answer leaves you down a four-mana 2/2 with nothing banked. Where the swarm holds together, though, it converts width into a single threatening attacker without asking you to attach a separate anthem; the Moa is the anthem, paid out one entry at a time.