Trostani, Selesnya's Voice

Populate gets its mascot here, and the choice to attach a lifegain engine rather than a combat ability tells you exactly what the mechanic was built to enable. Every other creature that enters under your control pays out toughness as life, which means the token-copying activation feeds itself twice: each populate adds a body, and that body's arrival refills the buffer that keeps you alive long enough to do it again. The 2/5 frame is deliberate. This is not a creature that wants to attack; it is a creature that wants to survive on a stalled board while it duplicates your best token over and over, and the high toughness keeps it standing through the kind of incidental damage that a go-wide token deck invites. The activated ability copies a creature token specifically, so the sequencing runs the other direction from most engines: seed the board with the right token first (a beater, a flier, anything with a relevant body), and only then does this turn that one good token into a recurring resource rather than a one-off. What balances the engine is that it does nothing in a vacuum: with no other creatures entering and no token to copy, it is a 2/5 wall that gains zero life. The payoff scales precisely with how much token machinery sits around it, which is the cleanest possible statement of what a populate commander is for.