Mariotale: Lumalovania

This takes place in a Mariotale AU with the following swaps:
Mario & Luigi = Sans & Papyrus
Peach & Daisy = Alphys & Undyne
King Boo = Napstablook
Bowser = Asgore
A random evil shape-shifting robot = Flowey
Smithy = Photoshop Flowey
Croco = Muffet
Rosalina = Gaster
Lumas = Gaster followers
"Lumalovania", as shown below, is played during the final Mario fight on genocide. Rosalina and Mario will judge your actions at this point in the game, and if your LV is as high as possible at this point, Rosalina will transform Mario into Galaxy!Mario, who you must fight. 
HP: 2147483647 (>216 perfect hits)
DEF: 32767
Overall, much harder than Sans, as he can dodge as well, while still requiring many hits to defeat. Has both high natural damage (255) and KR, so even your max HP of 32767 will be depleted fairly quickly if you are not careful. You won't die if you stay still during the entire first attack though, unlike the normal Sans battle.
If you manage to defeat Galaxy!Mario, you then instakill Bowser and proto-Smithy. Rosalina then makes a final statement and fills the screen with 9s, and crashes the game. (There is no equivalent to demon Chara)