Event Horizon

Celestial spells you cast cost {3} less.
Colored spells your opponent casts cost {2} more.
When a creature attacks you or a Planeswalker
you control, exile it at the end of combat. At the beginning of each end step, if there are ten or
more creatures in the exile zone you may pay {10} and sacrifice Event Horizon. Return all
creatures in exile to the battlefield tapped under
your control.