The Sanitarium tells each player to draw a card, but the Comprehensive Rules tell us that when multiple players are instructed to draw a card (like here), the Active Player will perform all their draws first, and then the Non-Active Player does the same (and in multiplayer, the draws are turn order: AP first, then the Non-Active Players in turn order). For Geier Reach we’re only drawing one card, but if it told each player to draw 2 cards, the AP would draw both before the NAP draws any, for example. Next up is the discard: each player makes their choice in turn order (so AP makes their choice first, then the NAP does the same), and then discard simultaneously. This is so you can’t decide what to discard ‘based’ on what your opponent discarded- you make that choice before you know theirs. The easiest way to do this is to have each player select the card they’ll discard, and place it face-down on the table to clearly denote it as ‘the card I will discard’, wait for everyone to have made said choice, and then perform the discard simultaneously. Et voilà, you are done activating the Sanitarium!
But wait- what about Madness? Well, if either player has discarded a card with Madness, it’ll get shunted into exile thanks to the replacement effect on Madness. If just one player ditched a Madness card, that trigger will go on the stack, and we proceed as normal for Madness: each player will get priority to respond to the trigger at least once, and once everyone passes priority without adding to the stack while the trigger is on top of it, it’ll resolve. The controller will either pay the Madness cost to cast the spell, or decline to pay that cost and the card will go back to the graveyard. If BOTH players discard a card with Madness, we just use AP/NAP order; the AP places their trigger on the stack, then NAP does the same. NAP’s trigger will resolve first, and cast their spell, and then after that spell has resolved or been countered, AP’s Madness trigger will get to resolve.
Finally, what if you’re activating it while you’re in topdeck mode, hoping to cast whatever you drew? Well, unless it has Madness or Flashback, you’re gonna have a bad time. Nobody has priority in the middle of resolving a spell or ability, so the only way to cast a spell at that time is if you’re given explicit permission to do so by the spell or ability (like with the trigger on Goblin Dark Dwellers, or the entirety of Epic Experiment). You are given no such permission here, so you’ll simply draw and then discard the card you drew, since it’s the only card in your hand.
Today’s Rules Tip was written by Trevor Nunez