Primal Evolution

As an additional cost to cast this spell, sacrifice a
creature.
Search your library for a creature card with
mana value X or less, where X is 1 plus the
sacrificed creature's mana value, put it onto the
battlefield, then shuffle. Target opponent
searches their library for a creature card with
mana value X or less, puts it onto the battlefield,
then shuffles. Then those creatures fight each
other.