Deltatraveler Hardmode - Finding the "Egg" and Kris's Knife
After meeting with Toriel in her house (not sure about the specific flag), it's possible to backtrack all the way to find an NPC that will give you the "Egg", and also Kris's Knife at the beginning of the Ruins.
During the obliteration route, there's a different cutscene for picking up the Knife.
Also, neat thing i just discovered by doing this, after meeting Toriel and going back, ALL enemies will despawn, doesn't matter if they were spared or avoided.