Rakdos, the Muscle
Most sacrifice payoffs in these colors pay you in life loss, card draw, or a body somewhere on the battlefield; this one pays you in cards off the top of a library, priced by what you fed the machine. The mana value of the sacrificed creature becomes the size of the exile, so the ability rewards throwing away expensive fodder rather than the usual one-drop chaff: sacrifice a five-drop and dig five cards deep, and the "mana of any type" clause lets those cards cast without color constraints until your next end step. Note the target is "target player," not an opponent: aiming the trigger at your own library turns the engine into a temporary card-advantage burst off your own deck, no fixing required, while pointing it at an opponent doubles as incidental library theft. That flexibility is the real wrinkle. The built-in outlet completes the puzzle. Sacrificing a creature to gain indestructible and tap itself both protects the body through a board wipe and, crucially, supplies the sacrifice this card needs to feed its own trigger without an external outlet. The once-per-turn limit and the tapping stop it from spiraling into a repeatable engine alone, so it wants a wider aristocrats shell around it. It is a payoff that asks you to value your creatures by their mana value on the way to the graveyard, not by what they do while alive.
