Pure Intentions

If a spell or ability an opponent controls causes a player to discard multiple cards, such as Waking Nightmare or Three Tragedies, Pure Intentions doesn't return to hand until its triggered ability has resolved. A player can't discard the same Pure Intentions twice for the same discard effect.

Neither part cares who decides which card to discard — only the controller of the spell or ability matters.

The first part of Pure Intentions is the effect of casting Pure Intentions. The second part is a triggered ability that triggers whenever an opponent's spell or ability causes a player to discard Pure Intentions.