I got into it today. The attacker declared an intrigue challenge, and tried to trigger Altar of Fire, but I used Misinformation. He said, since he had first action window, he could trigger his first, meaning that he got to use a card that triggered on him winning a challenge when he in fact lost. Please tell me this isn't the case. I will probably go crazy.

DieMyDarling said:

So even in his "I get to trigger Responses first" reasoning, Misinformation still comes first because it is a cancel effect to determining the winner of the challenge - and cancels for something will always come before regular Responses to that something.