Ok, so I started (but didn't finish) a genocide run.
Yep, the grinding part was boring, as expected, specially in the ruins and snowdin. The battles against Undyne and Sans were worth it, though.
Undyne's battle was hard but I expected it to be harder. The exclusive attacks were super fun.
I also didn't skip Muffet's fight because it's really good. I didn't use items on it, though.
Sans took around 2 hours and 45 minutes to die (at least it didn't beat Gamma's record which was 3 hours). But after killing it I didn't finish the run. I went back to some locations to see if anything changed but I didn't find anything. So I reset the game and fought Sans again. I didn't die, but I stopped the game when he fell asleep.
Then I started again and got dunked on. Wonderful.
Yeah, I'm still not going to finish this run beyond that. The fact that someone has to give Chara their soul to keep playing actually bothers me, spiritually. I mean, they talk to the player directly. So maybe they're giving their soul for real. Or maybe not. It still bothers me.
EDIT: Weird, I was using the burnt pan, not the knife. But I still got a knife animation when Sans died.
EDIT2: Agh, I meant the ballet shoes. The burnt pan can't be obtained in this route.
EDIT3: Wait, it WAS the burnt pan. The one that can't be obtained is the stained apron. I'm an idiot.