ok i know what the problem is for the troll-face sans. if you press special 5 times before the match starts the troll-face is enabled. it also enables when you are fighting a Ronald. this happens unless you are using an alternate skin for him. just don't press special until after you can move, and then it will not have the troll face. this is just an easter-egg in the code put in by the developers if you didn't follow the bad time instructions. so in a way, yes it is normal, and it is not a glitch (i don't even know if it could be counted as a glitch anyways if it was unintentional).

to sum it up, if you are default sans skin when fighting someone else, and you press special 5 times before the match starts, or you are fighting a Ronald, you will have a troll-face skin instead.

i hope this solved your questions.

edit: this happens with all skins, so it actually was just
"a little trolling."

it was a joke put in by the developer to prank people if they pressed special 5 times before the match started, just like the instructions said to do for hard mode. it was a prank.

also the Ronald thing was a guess since of another report of this happening. i tested it and it does not rely on Ronald. it only relies on if you do or don't press special 5 times before the match starts. i hope this solved your problem