you open Super Smash Bros. Ultimate on your switch, then get sucked into the game. You wake up in a dark room with one swinging light. You see the Mii Gunner sitting on a stool, in the Cuphead outfit, but not the headpiece. The sans outfit is on the ground next to her. She looks at you with desperate and slightly insane eyes.

(Mii Gunner): "don't forget about me... please don't forget about me..."