Notes

• Sans is from the True Pacifist route, after they've gotten to the surface and integrated with humans.
  
• Most of Sans' laziness comes from apathy. If the timeline is constantly reset where no one remembers anything (and he only knows it was reset, not what happens), then what's the point of putting effort in? It's also the reason why (in the Genocide Route) he never stepped in until the end. He simply assumed it would be reset again, just like it had been before. In essence, it didn't matter what he did because there would be no consequences or benefits to it; even if he tried to protect Papyrus, there would just have been a reset and Papyrus attacked when he wasn't there. The fact that his readings proved that time would simply stop is what pierced through the apathy to get him to move.
  
• Because of this, Sans is more active now that he's on the surface and prone to doing more things just in general. He's still got fairly low stamina and tires somewhat easily, and he still adores napping or relaxing, but he isn't anywhere near as "lazy" as he first appeared. Unless he wants to mess with Papyrus, and then he'll play it up.
  
• Combined with this, he's also more willing to engage in fights if necessary, though he prefers to hold back when he can. Since he's outside of the "resets" cycle, he knows there's no guarantee that things will be fixed if he stays inactive, which means not stepping in to help could have actual, real consequences.
  
• The idea of consequences scares the living shit out of Sans. He's existed for a long time (to him, if not chronologically) not bothering or caring about them, because in the end they just wouldn't matter. However, now that they're out of the underground -- where he knows the resets repeatedly happened -- he can no longer expect things to clear up. It's freeing in one way, but also deeply terrifying.
  
• Because of said constant resets, he's also deeply paranoid about it happening again despite Frisk's promise not to. This sometimes manifests in brief panic attacks when waking up somewhere "familiar", at least until he can think and realize he remembers everything (meaning there was no reset).
  
• He has nightmares about the Genocide Route, sometimes foggy, sometimes crystal clear. He's fully aware these nightmares are most likely a different timeline; Sans isn't the type to get nightmares easily, after all, and his dreams aren't as vivid as those specific "memory-nightmares". Being Sans, however, he doesn't tell them to anyone, especially since a lot of his fears revolve around Papyrus' death and Chara.
  
• Some datamined information.
  
• Sans adores the ocean at night, especially during rain. He also loves the night sky and stars, all for the same reason - the beautiful glittering they do.
  
• He has a habit of helping out stray animals, much to Papyrus sometimes dismay (considering how much of a mess it can lead to before Sans takes them somewhere else or when he comes back dirty).
  
• With the resets no longer happening, he's extremely inquisitive, curious, and loves to travel and catalogue what he sees in a journal (complete with pictures).
  
• He also loves to collect things - shells, rocks, anything that seems memorable.