Leech Breeding

{t}{b}{b/g}: Create a 1/1 black and green Leech creature token with wither.
{t}{b}{b}{b/g}{b/g} Sacrifice a creature: Create X 1/1 black and green Leech creature token with wither, where X is equal to the sacrificed creature's toughness.
{t}{b}{b}{g}{b/g}:Sacrifice X Leech tokens, target creature gets -X -X until end of turn. If a creature would die this way, exile it instead.