Yo I'm starting to think that Pap may have a teensy bit of Determination like Undyne and Sans. If you kill him, his body disappears instantly but /his head doesn't until much later/. He stays alive as a head to give you several last sentences before he dies for real. Now, he's not the only other monster who sticks around after being drained to 0HP (see Toriel & Asgore), but it's strange that he stays conscious even after most his body has been turned to dust. idek about this but... (pt.1)

The fact that Sans had to remind himself to not forget suggests that him and Papyrus are forgetting Gaster. And wouldn't that be better? For Papyrus to allow himself to forget what he did, to stop the sensation of his sins crawling on his back when he travels with the River Person. He tries to sleep as little as possible because when he sleeps he sees Gasters death and he tries to ignore the feeling of being watched in Waterfall, but try as hard as he can, Papyrus remembers more than he'd like.

"What if that would hurt him more though? Like… I feel like he might take that as 'Despite how hard you try, you’ll never change what you are.'" i knOW I REALIZED AFTER I SENT IT. Now I'm imagining Frisk finding out about his past somehow and saying this to him because it always helped THEM get through things. They say it with completely sincere and good intentions but he just... looks down, weakly nods and shakes as he's trying not to let tears spill and oh no I hate myself so much

What if when you kill papyrus and reset and sans says "here's some advice on fighting my brother: don't" He's really trying to save /you/ because he isn't sure if papyrus will remember between resets and attack you first?

I'm desperately hoping you're reading too much into this bc Papyrus deserves happiness and this theory is so sad (it is well put together, however).

I've honestly thought for a while that Pap could actually be just as depressed as Sans, just better at hiding it. I mean, it wasn't for the same reasons as it is now, but still. It makes a lot of sense honestly, living with what grief and blame he may have, along with forcing a smile to make sure his brother makes it through the day can't be easy for one, young adult skeleton

I just realized something that blows a hole the size of your theory in your theory that Papyrus is aggressive and kills people, and that Sans would try to prevent him if he tried to kill again. I present to YOU.... THE GAUNTLET OF DEADLY TERROR! Pap turned it off of his own accord, and Sans merely waits patiently for the Player to die- even nonchalantly and jokingly saying that 'it doesn't look very activated'. clearly Pap could not kill- and, mind you, there are no signs of a breakdown before -

Okay you know what I'm going off anon because this is important to me. Everything Pap has done has a different meaning now... like what if one reason he sent Alphys home early was because she said stuff about herself that hit too close to home? Flowey may have had something to do with it too but what if he also just couldn't bear to have the words he worked SO HARD and so LONG to stop saying to himself thrown back in his face? (now that I think about it they're more alike than I thought) (pt.1)