Undertale: Meltdown Imminent would be a hypothetical Genocide core fight against Sans where he tries to keep you occupied while Alphys melts down the core (with you still in it) [Helps me practise normal battles]

Undertale: Blooky's Rage would be a hypothetical Genocide rematch against Napstablook taking place right after you kill Sans [Helps me practise survival battles]

Undertale: Cyan Would be A short take on the Cyan soul's experience in the Underground

(edit: I have some in my opinion pretty cool ideas for this, so if this isn't the winner I might consider making a full game based on this concept)