Keon, the Interrogator

Whenever a player casts an instant or sorcery
spell, put a memory counter on Keon.
{1}: Remove X memory counters from Keon.
Cast an instant or sorcery spell from a graveyard
with mana value X without paying its mana cost.
If that spell would be put into a graveyard, exile
it instead. If the spell was cast from your
graveyard, draw a card. If the spell was cast from
an opponent's graveyard, that opponent
takes 2 damage.