Hi. I'm not really interested into speedrunning this game, but I found this glitch during my genocide playthrough, and I was wondering if it could be of any use.

The glitch is fairly simple: If you press a direction when the game window loses focus, the character will walk on place, without moving. You can then only continue in the given direction, or not move at all. The direction remains locked after the window take focus again, until you press the direction (here left).

If it is something well known, well, sorry for the annoyance.

EDIT: Oh and when the character is walking on place, random encounters occur as if you were walking normally

I think it's known yeah. Some people have used it to farm the Glyde encounter in the Snowdin cave which usually takes about 4 minutes or something so doing this makes it a bit less tedious. Otherwise I'm not sure where else it's useful.

No annoyance whatsoever, and someone might eventually find another use for it! :)