Plankton, The Krab's Scourge

Flying

When Plankton enters, each player exiles the top X cards of their library, where X is the amount of
mana spent to cast Plankton.

Whenever Plankton attacks, you may cast an instant or sorcery spell from among cards exiled with Plankton without paying its mana cost.

I can't help it, I'm a kleptomaniac!