Workhorse

A creature whose entire body is its mana reserve. The 0/0 base print is the whole trick: the four counters that keep it alive are the same four counters it spends to make mana, so every point of colorless it produces is a point of toughness it sacrifices. Crank it for all four and it dies as a state-based action, returning four mana for the price of a creature that briefly existed. That self-cannibalizing structure made it less a mana rock than a sacrifice payload disguised as one. The counters give it a death timer the controller sets manually, which is why it found a home anywhere a graveyard or a sacrifice outlet wanted artifacts to feed and mana to launder. Pair it with a way to add counters back and the engine never has to stop; pair it with proliferate and the math tilts further in your favor. What it accomplishes mechanically is an early experiment in encoding a creature's life total and its utility into the same resource, the kind of tension later cards built whole archetypes around. The body is incidental. What Workhorse really is, is a four-charge battery wearing a horse for legality, and the question it always poses is how much of itself you are willing to spend at once.