For a certain watcher's sake...
[HIDE]That Worm was Cassisworm, who was disguised as Reji Nogi. As you've seen, he's a natural fighter. He possesses the "Life of Immortality" ability, which allows him to revive and evolve into a stronger form. And each form has a unique power-up to it.
The 1st form he takes is Cassisworm Dimidius. In this form, he possesses the "freeze" ability, allowing him to stop the flow of time. This power makes even Hyper Clock-Up useless.
The 2nd form he takes is Cassisworm Gladius. In this form, one of his arms grows a blade, and he gains the "absorb" ability, which allows him to absorb the powers of other Worms, as well as Tachyon energy from the Riders.
The 3rd, and final form he takes is Cassisworm Clipeus. In this form, he retains the blade arm from his Gladius form and gains armored plates and shields over his body. His ability in this form is "clone". This self-explanatory ability allows him to make a clone of himself.[/HIDE]