So, that's creepy and Sans disapproves a lot. What the heck, Rainer! As Sans follows this skeleton and comes to the realization that this is a copy of him, he is sufficiently freaked out enough by this that he is now committed to following this skeleton extremely aggressively.

So: he uses haste and then activates blink to zip in through that door before it closes, one after the other because he is still keeping digital phantom active. Is Rainer in here or is the skeleton alone or what, what is happening Sans doesn't like it!!!