6. Five Nights at Freddy's: Specifically "Security Breach", as it's the one where the animatronics are the most fleshed out as characters. INCREDIBLE meme potential, and I'd consider it more likely than Undertale if not for the difference in devs.
Most likely candidates: Roxy, Vanny, or any Glamrock

5. Undertale: I don't need to explain this. It's a hit indie RPG primarily starring monsters. I consider this one of the least likely options due to it being both popular & welcoming to all ages, while Monster Prom decidedly isn't.
Most likely candidates: Sans, Undyne, Alphys, or even Papyrus.

4. Slay the Princess: A horror & romance themed visual novel that's recently boomed in popularity, and I HIGHLY recommend! Keeping things low-spoilers, the Princess ABSOLUTELY qualifies as a "Monster Girl". This would be my second most wanted next to SFL.
Most likely candidates: The Princess/

3. Hades: A wildly popular indie roguelike with romance elements which, while not "monster" themed, is obviously mythology inspired and is known for it's hot characters. I would've considered this more likely than Cult of the Lamb tbh.
Most likely candidates: Either of the protags.

2. Awaria: A ghost-girl themed puzzle game created by Vanripper, who has already had a guest character in Monster Camp in the form of Modeus from Helltaker.
Most likely candidates- Zofia Zmora (most important ghost girl), Ula Usterka (protagonist), other ghosts marginally possible.

1. Sucker for Love: An anime-inspired monster-girl dating sim themed around lovecraftian waifus, which had a new game release just last year and whose lead dev has been vocally supportive of Monster Prom's releases.
Most likely candidates (in order)- Ln'eta, Darling, with the others unlikely.