by Hermjard
From the Rules:"DISCARD: Monsters immediately resolve these then discard them."
"Purchased cards are immediately replaced from the top of the deck."
So, what is more immediate, replacing the bought card, or resolving it?
Because the way, you resolve a bought card (chosing targets etc.) could depend on the cards, which are available, it's important to know, if a bought card is resolved before or after the new card is visible.