Regibald, Teaching Wizard

Whenever an opponent casts a spell from their
hand, each other player discovers X, where X is
the amount of mana spent to cast that spell.

Whenever you cast a spell from your hand, exile
the top card of your library. You may play that
card as long as Regibald is on the battlefield.

The first spell you cast from anywhere other than
your hand on your turn has demonstrate.