Dauthi Voidwalker

3 human commander game.

Early in the game, I cast Fierce Guardianship for free. It was exiled to Dauthi Voidwalker. Later in the game, a Toxic Deluge was cast by player 2, and player 3 controlling the Dauthi Voidwalker activated it. He attempted to cast Fierce Guardianship. He was unable to cast once he targeted it. We even tried rolling back the extensive turn, but both attempts failed.