Mortarion, Daemon Primarch

The self-inflicted wound turned into a resource. The end-step ability caps token production at the life you lost this turn, which reads like a limit until you notice how much black wants to bleed itself anyway: fetchlands, painful mana rocks, tutors that cost life, and the whole suite of "pay life to draw" effects that mono-black leans on. Mortarion converts that expenditure into a menacing swarm at the exact moment the loss is already tallied, so the deck stops treating life as a countdown and starts treating it as fuel. Because the trigger only counts life lost during your own turn, the sequencing rewards a proactive turn spent activating painful abilities: you spend the life first, then charge the mana as an afterthought before passing. That timing is the entire trick. Where most token engines ask you to invest mana up front to build a board, this one asks you to have already suffered, and prices every point you were going to give up regardless. The Nurgle flavor points the same direction: this is the Primarch of plague and decay, and the card rewards sickness accepted and slow rot cashed in rather than defended against. The flying 5/6 body is almost incidental. The reason to run it is the way it turns life total from a bar you protect into a currency you spend deliberately, and hands back a wave of menacing bodies for the trouble.