Mephodos, the Eternity

Flying, Shroud, Indestructible, cannot be exiled, cannot be sacrificed
Whenever a creature attacks you or a planeswalker you control and Mephodos, the Eternity cannot be assigned as a blocker, assign Mephodos, the Eternity as a blocker instead.
If Mephodos, the Eternity would be put into your graveyard from the battlefield, put it onto the battlefield instead.