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 creation of intelligent magical weapons is not an exact science and there are occasional failures, as such think of causing a little more stress to your players by "rewarding" them with an insane magical weapon
Agrophobic, refuses to come out of the scabbard without a strength check to draw it.
Haemaphobic: afraid of blood, fight at a penalty against any blooded creatures but really good against undead, elementals etc
Schizophrenic, not just one mind in your sword, lets have half a dozen minds in there, all different and bound to cause confusion
the possibilities are endless