lost caverns of ixalan set booster box The Collector – Mox Boarding House A special bonus card from Magic’s history can be found in 25% of packs. MTG / The Lost Caverns

Specifically, whenever an effect asks you to draw a card and your library is empty, you lose the next time a player would receive priority (which, in practice, pretty much means on the spot , regardless of what's in play or on the stack)

This will be the only time ever you hear me claim a Saitou as a particular favorite within a subset

You then get to bring back a creature card with a mana value less than or equal to the amount of life you gained from the graveyard to the battlefield

That means more creature tokens, more +1/+1 counters, more loyalty counters on planeswalkers as they enter, and more of whatever counter-based nonsense your deck has chosen as its profession