Requested by Martin - Susan (accidentally dressed up as Counselor Troi) meeting Elliot (in a cat costume) and Ashley (in an adorable mouse outfit). Costume parties exist, iirc.
I'm not sure how Elliot and Susan got that close without seeing each other, how neither of them realized they were going to the same costume party, OR how Susan actually managed to accidentally dress as Counselor Troi from Star Trek: The Next Generation, but this is clearly a thing that has happened and they're just going to have to deal with it.
(Sidenote: Those feet on Ashley are clearly part of her mouse costume. Clearly and obviously. So clear and obvious, in fact, that it makes no sense that I felt it necessary to write this, and I should clearly and obviously and for reals just delete it, but I'm leaving this in for reasons)
Note: Requests are paraphrased for clarity and brevity