These are some of my favorite ideas. I will run one of these someday.
What motivates intelligent monsters? Do they simply lie in wait in dungeons and tombs so that some brave adventurers can come along and kill them? Of course not. They do things. They have goals or instincts. This adventure is about what monsters do.
Each of the PCs is a monster. I’m thinking classical monsters, so a vampire, a werewolf, a ghost, and flesh golem (Frankenstein). It will probably take some level magic to make them all relatively equal. They’re all some alignment of evil, but they’re drawn together (bound by magic, maybe?) to reach a distant castle for a macguffin.
Along the way they’ll have to pass as people, terrorize a village, and (of course) fight heroes. This is the kind of adventure that would probably play well in Ravenloft. Really, the monster PCs won’t be that much different from regular PCs in a Inner Sea or Forgotten Realms campaign, and that point should probably be driven home.
Monster Mash 2
I’m a funny person, so this is a play on words. Everyone is a barbarian with a giant hammer, and the whole adventure is smashing tons of low level monsters to death. Just mountains of skeletons, zombies, goblins, orcs, giant spiders, anything you can throw at them in large numbers. Really stretch the limits of CR increasing with numbers. Make it a point to describe the heaps of dead monsters. Make them really question where in the hell did all these monsters come from. Keep a kill count, give a prize to whoever smashes the most! Give them lots of locked treasure chests to smash with hammers, and make one of them a mimic, so, for the first time ever, the players surprise the mimic.
So while Monster Mash was about playing monsters, Monster Mash 2 is about mashing monsters. Ha ha.
Super Monster Mash
Okay, we know what player sized monsters do. But what to big monsters do? In Super Monster Mash, each of the players is a Huge monster. So uhh what do they do? Eat smaller things. Trash a town. Fight. I didn’t have many plans for this one, except that it should end with some kind of kaiju battle.
And that’s that! Those are my unused D&D ideas. I hope they inspired someone, and I hope someday I can do something with them myself.