Xera, Knowledge Refiner

When Xera, Knowledge Refiner enters the battlefield, each player creates Omphalos, a
legendary blue enchantment token with "At the beginning of your end step, each player draws a
card, then discards a card."
Whenever a spell or ability an opponent controls causes you to discard a card, you may put five
cards from your graveyard on the bottom of your library. If you do, you gain 3 life.