When you kill Muffet, there is an extremely lengthy unskippable cutscene where a smaller spider scrolls on screen, back off, and then gets a flower and does it again. It's like 20~ seconds. Since you need to abort Genocide at some point in Core, and because the spider donut instantly spares Muffet without the cutscene, doing this is the fastest way to progress.
The other thing is with Neutral Glitchless you have to abort Genocide run eventually. You have to spare a boss somewhere, and Muffet is the last possible boss you can spare to abort. If you kill Muffet I believe you are stuck on Genocide.
To address Twitch's new 100-hour highlight limit, we are making a few changes to make sure that the highlight limit (as well as any future Twitch decisions) doesn't affect the leaderboard's integrity. Effective immediately, we are no longer accepting runs submitted through Twitch highlights, reg