If you can't exile Underworld Cerberus when its last ability resolves, perhaps because it's been exiled by another spell or ability, each player will still return all creature cards from their graveyard to their hand.
2013-09-15
wotc
If two of these die at the same time, the last ability of each will trigger. If each player controlled one, the nonactive player's ability will resolve first. The Underworld Cerberus controlled by that player will be exiled, and all other creature cards in graveyards (including the Underworld Cerberus controlled by the active player) will be returned to their owners' hands. Then the active player's ability will resolve. That Underworld Cerberus won't be exiled, but any creature cards in graveyards at that time, perhaps because they died in response to this ability, will be returned to their owners' hands.
Format Legality
Standard
Not Legal
Future
Not Legal
Historic
Not Legal
Timeless
Not Legal
Gladiator
Not Legal
Pioneer
Legal
Modern
Legal
Legacy
Legal
Pauper
Not Legal
Vintage
Legal
Penny
Legal
Commander
Legal
Oathbreaker
Legal
Standardbrawl
Not Legal
Brawl
Not Legal
Alchemy
Not Legal
Paupercommander
Not Legal
Duel
Legal
Oldschool
Not Legal
Premodern
Not Legal
Predh
Not Legal
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