There is a half dead crow in the attic s5e5. We don’t se Martin hammer it in the head, but later we see the dead crow. Not emotional, but shouldn’t watch if you don’t like to see dead animals.
It wasn't just the plushie being destroyed. The whole episode is about two brothers. One is trying to find the stuffed animal to destroy it in front of his brother. His brother is very stressed the entire time. Really the suspense of what was going to happen to the toy was what made me nauseous.
One character is confirmed to be autistic with an interview with the actor. People’s treatment of said character throughout the series is questionable, but it comes across as humorous.