#1 Fanon:

Name is Mettaton. He is a human.(Or a ghost with a robot body)

Canon:

Name is Mettacrit. They are a ghost.

#2 Fanon:

Asriel has a special laugh.

Canon:

He doesn't have one.

#3 Fanon:

Undyne is a robot. Other forms are EX and NEO

Canon:

(Pre-reboot) Undyne is a cyborg. Other form is ULTRA.

(Reboot) Undyne is a fish. I don't know if she has another form or not.

#4 Fanon:

Shift personalities.

Canon:

Does not shift personalities. 

That is all for now.

Storyshift by Voltra