I guest star in Jan's video, but fair warning, I have a hard time keeping my mouth shut, so there are some hints to spoilers, but I tried to keep them as vague as possible.

Also, I don't know what the secret ending you're talking about is, but there are multiple, multiple neutral endings. One for genocide except whiffing on Mettaton NEO, one for killing all of the bosses and only the bosses, and more. I'm actually planning on, if/when I get it for myself, playing pacifist, then slowly going one kill at a time towards genocide, until I've gotten every single possible outcome.