Collector of Lost Souls

When Collector of Lost Souls enters the battlefield, you may pay {x}{b}.
If you do, target opponent reveals their hand and
you choose a nonland card with converted mana
cost X or less from it. Exile that card. You may
cast that card for as long as it remains exiled, and
you may spend mana as though it were mana of
any color to cast it.
Whispered bargains, stolen secrets, and forgotten sins
are its treasured rewards