Bards singing, and playing Safty dance, and or Enter the sand man.
Half Dragon Half Horse Monsters.
RPG guild mods, but as a another group of rival adventures.
Code Guru, but as a Lich(because we all know he will never die, till we find what he hid his soul in.)
Time traveling Brock-o-Bomba, and dick chainy with a gun.
A Giant White killer rabbit.
The Joker from batman
Batman I doubt even level 20 epic party of 6 or more could beat batman.
A car full of clowns(30 or more)
Any member of the crew on SS13
The pyscho(s) from outlast.
Those main charterers from Cowboy bebop.
Discord(MLP) or Chrysalis Queen of the Changelings
Snape, or anyone else from harry potter, who might be funny to fight. (THAT 10 POINTS FROM GRIFFONDOR!)
Undead Houses(Houses once alive, then died, and are now brought back to life. So Zombie/vampire/*input type of undead here*)
Screaming Raging Cod nerds.
Something from Digimon.
He-man AND THE MASTERS OF THE UNIVERSE!(DO-DO-DO-DO-DODODODODODDO-DOD-DOD-DO-DO!)
Dr Who(actually that's just "The Doctor" )
Rabid Forming at mouth crazy Kurt Cobain.
Evil Music instruments(you don't want to know where it going to shove itself)
THE GOD OF RUSE!
GIANT SPACE RABBITS!(FROM MARS!)
Any other suggestion spam?