you walk down last corridor, it's different though, it's a Dark blue shaded, and some of windows are shatterd, you then hear sanses voice near a pillar he is most likely leaning on it.

Sans: Heya kid, apparently death isn't enough to stop you, so I prepared a little surprise for you. It took me a few months but... You see sans open his eyes but both his eyes are glowing a bright Blue. eh nevermind... Just let me know when you give up, Kay? he lazily points at you, clearly not taking you seriously.