It could be about the life of Sans and Papyrus, in Snowdin. It could be like a sitcom. And maybe like Grunkle Stan in Gravity Falls with his secret brother later to be revealed, Sans could have his secret of knowing about resets, and how everything will always be reset at some point. At first, the series will just be a funny gag every episode about Sans and Papyrus living in Snowdin until later on the series becomes a lot more darker when The Human (Frisk) shows up and does a genocide run, it more focuses on Sans at this point and his secret of knowing about resets. After that, it shows the aftermath of Papyrus and it shows Sans's reaction to that, which he would sad (obviously) since his life is just a repeating loop of this in a game, and then finally Sans faces The Human. And dies trying, but he doesn't care about his death since it will all just reset, so that's my idea for the series.