Filius Flitwick

Professor (Whenever a nontoken creature enters the
battlefield under your control with a lower toughness or
power than this creature, put a +1/+1 counter on it.)
Whenever Filius Flitwick blocks or is blocked
you may cast an instant or sorcery spell from
your hand or library without paying its mana
cost. If you play a spell from your graveyard in
this way, exile it.