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.
Cards you cast with tome counters on them gain
replicate. the replicate cost is equal to that cards
manacost - {x}, where x is the amount of cards
you own in exile with tome counters on them.