I just played a PvP match against an undercovered Riri, a Polaris and Dr. Thor using two 560+ boosted 5* characters and after about 3 rounds I was basically stunlocked out of playing the whole match. I got to make about 2 more matches the whole game. You may need to reconsider the interaction of these two characters or we will have a Bishop issue but just worse since you can't just mirror match this and you need both characters to even try, thereby narrowing the people who can use this (unlike Bishop). Not being able to play the game is not fun....we have been through that (please see Bishop issues from the previous developers).
Dr. Thor I guess kept destroying her tile and generating enough green charged AP for her to keep this stunlock cycle going.
Make it so she is stunned if her countdown tile is destroyed (rounds= to the countdown value left if possible) or you may need to consider making it so Dr. Thor cannot destroy friendly tiles.