The Soul Stone

Indestructible
The Soul Stone enters the battlefield tapped and does not untap during your untap step.
Exile 3 creatures you control: Untap The Soul Stone.
{t}: Prevent all damage dealt by attacking creatures this turn. All attacking creatures are exiled.
"And the Soul Stone... nobody even knows where that is! Therefore Thanos cannot get it, and he never will."
- Thor to Gamora.