First of all, build up 1,000,000 bolts. Then, go to planet Barlow, if you've already been to the Gadget Ron shop, you can use the elevator by your ship, if not, you'll have to fight your way there. Once your there, purchase the RYNO II. Then, once you get to planet Yeedil make your way to the Mutant Protopet. Use your swingshot to get to the last boss. First, it'll start rolling at you, stretch jump out of the way, keep doing that until it stops. At that moment, equip the RYNO II, target it, and hold the circle button. Your foe will be vanquished after about 5 seconds of blasting.