Undertale by toby fox
Terraform by coolboy6432 and LinkSans2000
papyrus is still believes in you in genocide.
There is no way that Disbelief Asriel can happen.
There is no Toriel genocide fight specifically, instead, Asriel&chara pretends to kill themselves and so on the geno route so Shifty can’t take their SOUL's, but comes back once Toriel is killed but chara absorbs toriel's soul while asriel absorb's the human soul's to fight Shifty. Eventually, Shifty overpowers them in the end
and chara soon absorb's asriel's soul too.
UndyneChan turns into a mech in the genocide route, having actually undergone the procedure to turn into a robot. Of course, it’s no match for the human’s sheer determination, and she’s quickly defeated.
Chara's Genocide is… well, I am making a fangame?
Sans try's to kill Shifty on the Genocide route but is stopped.
Echo still tells the story of what happened the night Mettacrit, him, and the Fallen Human died in the Capital during genocide. He’s killed at the very end as well.
Shifty crosses the barrier during Genocide. If it were a game, mettacrit and the Fallen Human would have a short exchange to the player about erasing the world together.