Karn's Temporal Blundering

(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.
Centuries ago, a quest to harness time nerfed every planeswalker in existence. Somehow this is Urza's fault.