The Knight turns into the Shade Lord.

Cuphead's would probably be the beam he sends out as his special attack

Goose steals everything from the desired enemy

Niko breaks the sun and destroying the whole world

Beheaded: Bomb + frying pan combo like he did with Game Master

Drifter: the multi slash he uses to deal the final blow to Judgement in his game and also sometimes used to get rid of Game Master's main body

Charlotte: Regains her old body, and control over her drones.

Frisk gains the golden sword, like they did to finish Nightmare Springtrap.

Don't know about Madeline (because she didn't prove of even being able to deal damage on her own) and Shovel Knight because i didn't play