Blood Pet

A 1/1 that exists to be eaten: the body is incidental, and the design is built around the line of text that turns it back into the mana you spent. The trade is mana-neutral with upside, since the creature can chump a turn or soak a sacrifice trigger before cashing out for the black it cost. Call it less a creature than a deferred ritual, a piece of mana you can hold on the board until you need it, with a body attached for the windows where the body matters. The design logic animates a long line of black sacrifice fodder: split the value into two events, the entering and the dying, and let a deck collect a payoff from each. The discipline that balances the rate is that the mana comes back exactly once, and only by spending the creature itself; there is no engine here, just a single round-trip. Black has reprinted variations on the pattern many times since (cheap creatures whose real job is to be sacrificed for resources), making this an early, unadorned statement of the template: a one-drop whose strategic axis is not what it does on the battlefield but what it leaves behind when it leaves it.