(You may cast a legendary sorcery only if you control a legendary creature or planeswalker.)
Target player takes an extra turn after this one. Return up to one target nonland permanent to its owner's hand. Exile Karn's Temporal Sundering.
You canâ€™t cast a legendary sorcery unless you control a legendary creature or a legendary planeswalker. Once you begin to cast a legendary sorcery, losing control of your legendary creatures and planeswalkers wonâ€™t affect that spell.
Other than the casting restriction, the legendary supertype on a sorcery carries no additional rules. You may cast any number of legendary sorceries in a turn, and your deck may contain any number of legendary cards (but no more than four of any with the same name).
If the target player or target nonland permanent is an illegal target as Karnâ€™s Temporal Sundering resolves, the other target is affected as normal and Karnâ€™s Temporal Sundering is exiled. If both targets are illegal, Karnâ€™s Temporal Sundering doesnâ€™t resolve and isnâ€™t exiled.