Their habit of eating moss
Huffing scented markers
Avoiding Asgore’s hug
Their euphoria after drinking hot chocolate
That fact that they’re selectively mute, only speak when spoken to, and their replies only being like 3 words long and blunt
Kris may be autistic/neurodiverse, due to how others talk about them. They’re lonely, socially awkward, sometimes do repetitive behaviors (flushing the toilet 100 times), they sometimes have odd ways of interacting with other people
I also headcanon them as an occasional user of sign language if verbal communication is hard for them in the situation they’re in
To any neurodiverse user on here, chime in if you like.