The End of Durin's Bane

Exile cards from the bottom of your library until
you exile a legendary creature card. Put that card
onto the battlefield, then shuffle all other cards
exiled this way into your library. Then, if you
control exactly one legendary creature, destroy
target creature with power 4 or greater.
"From the lowest dungeon to the highest peak I fought
the Balrog of Morgoth. Until finally, I laid down my
enemy and smote his ruin upon the mountainside."
— Gandalf