Extract Brain

Target opponent chooses X cards from their hand. Look at those cards. You may cast a spell from among them without paying its mana cost.

Slave of Bolas

Gain control of target creature. Untap that creature. It gains haste until end of turn. Sacrifice it at the beginning of the next end step.

Jeleva, Nephalia's Scourge

Flying
When Jeleva, Nephalia's Scourge enters, each player exiles the top X cards of their library, where X is the amount of mana spent to cast Jeleva.
Whenever Jeleva attacks, you may cast an instant or sorcery spell from among cards exiled with Jeleva without paying its mana cost.