Sethrion, of Watery Graves

Hexproof

At the beginning of combat on your turn, tap target creature you don't control, then it gains the following abilities: "Slumbering - Does not untap during your untap step.", "Awaken - Pay {2}: draw
a card.", and "When this creature Awakens, each opponent draws two cards."

The seas whisper of ancient leviathans, awaiting their return to the surface.