Trickster Darkin

Darkbond (You may pair this with an unpaired
creature an opponent controls when either enters the battlefield. They remain paired as long as they're both
on the battlefield.)
Whenever a creature that is paired with Trickster Darkin attacks, exile the top card if its owners
library face down. As long as it remains exiled
you may look at it, and you may play it. You may
spend mana as though it was mana of any color to
cast spells this way.