Whenever you gain life, Rodolf Duskbringer gains indestructible until end of turn.
At the beginning of your end step, you may pay . When you do, return target creature card with mana value X or less from your graveyard to the battlefield, where X is the amount of life you gained this turn.
Rodolf is a self-protecting lifegain payoff that doubles as a recursion engine: gain life to keep him indestructible and to crank up X, then each end step pay a trivial cost to reanimate a creature whose mana value is capped by the life you gained that turn. You build a board of lifegain sources, attack with an evasive 5/5 deathtouch-lifelinker, and grind opponents out by repeatedly returning your best creatures from the graveyard.
Rodolf is hard to remove—any incidental lifegain grants indestructible, blanking most targeted removal and combat
Built-in card advantage and reanimation that recurs every turn at a cheap cost
Flying, deathtouch, lifelink makes him a strong blocker, attacker, and Voltron threat all at once
BW has deep access to lifegain, sacrifice fodder, and reanimation targets
Reanimation X is gated by life gained that turn, so big targets require setup or burst lifegain
Exile, bounce, and -X/-X effects sidestep his indestructibility
Six mana means he comes down late and the engine doesn't start until you gain life
Vulnerable to graveyard hate, which shuts off the reanimation half entirely
Legendary Creature — Vampire Angel
. When you do, return target creature card with mana value X or less from your graveyard to the battlefield, where X is the amount of life you gained this turn.