All But One

Target one creature your opponent controls.
That creature gains indestructible until end of turn. Destroy all creatures, then target opponent loses X life where X is the number of creatures destroyed this way.
"That's the cruelty of the Black Knights of Rothan, they always leave one alive. As a mercy, or as a warning, we do not know, but the lone warrior always returns to his kingdom broken and shamed." - Captain Aligus of the White Knights of Krona