Evelynn, Agony's Embrace

Whenever Evelynn, Agony's Embrace attacks,
you may target a creature an opponent controls.
Target creature must block Evelynn, Agony's
Embrace this turn if able.
As long as you've cast no spells this turn,
Evelynn, Agony's Embrace is unblockable.
If Evelynn, Agony's Embrace were to leave the
battlefield for any reason, shuffle it into it's
owner's library.