Isildur’s Fateful Strike (LTR)

Card Text

(You may cast a legendary instant only if you control a legendary creature or planeswalker.)
Destroy target creature. If its controller has more than four cards in hand, they exile cards from their hand equal to the difference.

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Isildur cut the Ring from Sauron’s hand with the hilt-shard of his father’s sword, and Sauron himself was overthrown.