At the beginning of your upkeep, put two eon counters on Out of the Tombs, then mill cards equal to the number of eon counters on it.
If you would draw a card while your library has no cards in it, instead return a creature card from your graveyard to the battlefield. If you can’t, you lose the game.
If an effect instructs a player to draw multiple cards, each of those cards are drawn independently, and Out of the Tombs's second ability will apply to each one if appropriate.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.