If both players control a Knowledge Pool (“KP1” for active player and “KP2” for non-active player), you must keep track of which cards have been exiled by which Knowledge Pool, since the exiled cards are linked to that specific KP. For example, if I cast a spell from my hand on my turn, KP1 and KP2 will trigger. Since I’m the active player, KP1 goes on the stack first, followed by KP2. KP2 resolves first, so I exile the spell I cast (this is not optional) and may cast one of the exiled cards in KP2’s ‘Pool.’ Since that spell was cast from exile rather than a hand, neither KP will trigger again. That spell will resolve before KP1, when KP1 finally resolves, it will do nothing, since the spell that triggered the ability was already exiled, and you won’t get to cast anything from KP1’s ‘Pool.’

If one player controls both KP1 and KP2, he will essentially get to decide which ‘Pool’ a player will get to choose from when casting a spell, by stacking the triggered abilities so the ‘Pool’ he wants the player to choose from will be on the top of the stack and resolve first. He can use this to make sure his spells pull from the ‘better’ pool, and his opponent’s from the perhaps less desirable one.

Today’s Rules Tip written by
Ronny Alvarado, Level 2 judge from Houston, TX