Two creatures, forever cycling between the phases of the 5 elements, unable to rejoin.
The unnatural offspring of a zombie father and a human mother.
The excited, almost frantic sound of a mallet instrument erupts from the forest to your left. Within minutes, your party is confronted by a host of short, sprite-like gnomes clad in vivid greens and earthy browns. Attempts to communicate fall flat. The gnomes seem to ignore your words entirely, and you cannot understand the humming/whistling/snapping that apparently makes up their language. Luckily for you and your fellows, however, they don't seem hostile . . .
The PCs find a strange helmet, when donned it will take control of that PC and speak and act trough him/her. It explains that it is benevolent and needs their help in a quest and that it will stop possessing the PC when the task is done. Great if a player is gone for a number of sessions.