Yarm, Head Alchemist

Whenever a creature you control deals combat
damage to a player, choose a card in exile with
converted mana cost X or less, where X is the
total damage dealt this way. If that card has a
Potion counter on it, copy it. You may cast the
copy without paying its mana cost.
{g/u}{r/w}{u/b}{w/b},{t}: Search your library for an instant
or sorcery card and exile it with a Potion counter
on it.