Realm of Lost Memories

Realm of Lost Memories enters the battlefield tapped.
At the beginning of your upkeep you may pay {3} and tap Realm of Lost Memories. If you do, attach a creature from your graveyard to Realm
of Lost Memories as an enchantment aura.
{t}: add mana to your mana pool equal to the
mana cost of a card enchanting Realm of Lost Memories.