All the early Xevoz toys came with some mysterious accessory that didn't seem to be anything. It was basically just a little handle that served no purpose. Ah, but it did serve a purpose, just not one that any of us knew.
In February of 2004, Hasbro put out a press release hyping Xevoz. This press release had a little bit of background info that was never seen anywhere else:
A compelling story about a small but formidable fighting force known as The Xevolvers - the last hope of a planet plunged into chaos by a powerful technology. Long ago, the Ancients of XEVOZ learned to manipulate their genetic makeup at will with a device called the Evolutionary Accelerator (EV-AC). The EV-AC could change them physically, turning their limbs into tools and weapons of steel, stone, fire and even ice. One of the Ancients - the evil Genok - overthrew the rest and appointed himself ruler. The remaining Ancients formed The Xevolvers to stop Genok and imprison him in a secret impenetrable tomb for eternity. Or so they thought...
And then, here's a picture from the official Xevoz story bible:
That's a Xevolver using his Ev-Ac! So basically, the "mystery handle" is an accessory that was cut from the backstory at some point, but late enough in the game that the earliest releases still came with one.