I meant to update you awhile ago, but I wanted to let you know Mog and Ilya can exist in the same apartment now! They still have instances of Ilya hissing, mostly when Mog wants to play and she doesn't want to, but overall it's been good here! Thank you so much for your help in this matter. I've attached a photo of them even sleeping in the same bed.

I wanted to reach out and give you a (perhaps last) update on Landon and Punkin. 

They're been getting along pretty well since my last check-in. 

Right at the end of August, my roomies and I moved to a new apartment. I was concerned that this might create a setback, but actually the cats have gotten along better than ever in the new environment. There is still an occasional moment or two where they hiss, or one of them will get tense and I feel the need to separate them, but it's only been once or twice since we moved in. And amazingly enough, they've even been playing together a bit...chasing each other around the apartment, switching off and on between who's chasing and who's being chased.

When I leave for a few hours, or even a whole day, I now trust that they won't hurt each other. 

Thanks so much for your help! I feel like we successfully integrated these two and that with time, maybe they'll even become cat-friends.