Eruth, Demon Stalked Seer

When you cast Eruth, Demon Stalked Seer, you
may search your library and/or graveyard for a
card named Eruth's Tome, reveal it, put it into
your hand, then shuffle.
{t}: The next instant or sorcery spell you cast
with a tome counter on it gains replicate. The
replicate cost is equal to that cards manacost
reduced by {x}, where X is the amount of cards
you own in exile with tome counters on
them.