Kirby takes Cuphead's place in Cuphead's own boss fights. (Sorry for the bad storybook art i'm not an artist please don't bully me)
What you get
Play as Kirby against Cuphead's bosses: inhale their bullets and spit them back as stars.
Your charms become Kirby copy abilities.
Kirby's art and sounds come from your own copy of Kirby: Wacky Episode. The first Play spends about 15 seconds reading them before Cuphead opens. There's nothing for you to do.
Players
Solo.
Untested extra: with a second controller on the same PC, Keeby can take Mugman's place.
You need Cuphead and Kirby: Wacky Episode installed. Melty sets up everything else when you press Play.