basically, in this undertale take, once you get to the core, mettaton isnt there to fight you and sans isnt in the judgement hall, meaning you wont get love 20, so you cant do the deal with chara again, and you have to backtrack to find more enemies to kill. once you get back to hotlands, you see a cellphone outside of alphys' lab with 2 messages saying

"Sans, I have a plan, remember the DT extractor we worked on with gaster? Go down to the true lab and I'll try to turn it on and we might defeat the human"

"k"

and the elevator to the true lab works, and you go down there and you search for any amalgamates to kill, but they arent there

once you get to the place where you fight lemonbread in the pacifist route, instead of lemonbread being there, you will see sans waiting and alphys trying to turn on the DT extractor

*also you are love 13*

afterwards, you force them into a battle and there's 3 phases

on phase 1, its just regular sans and alphys battling you

on phase 2A, you fight sans while he got more powerful thanks to alphys' machines

on phase 2B, you fight alphys, the amalgamates and the DT extractor gets used on you, but it doesnt work fully, so you still have half determination, meaning you can still retry battling alphys and the amalgamates

cool or not cool?