Ninja Pirate Zombie Robot

To qualify for this, make sure the setting has at least 3 of the following: supernatural (e.g. demons, fae, or such), ninjas, pirates, vikings, undead (zombies, vampires, ghosts), robots/cyborgs, aliens or extradimensional beings, mutants
... depending on the included things the required number of elements may rise to 4 (e.g. aliens, robots, and mutants being in same game is hardly thematic breaking); qualifying with unlisted things can be done, though they are lesser examples of this concept.

Undead should not be able to cover both supernatural and undead category alone, even if they cross over in that (vampires and ghosts tend to do this).

The tag name comes from Kingdom of Loathing which seems to have popularized the concept itself somehow.

See also: crossover (when characters or things from separate established settings are thrown together)