After you can drive the Fourbie and after the Patchy event, you can go to Sly's Mountain Shack to upgrade purchased rangs. He also sells the Death Rang and the Doom Rang after you buy the Death Rang for 30,000 and 75,000. The Mountain is steep, so Sly added a lot of wood to help you.
At the top of the slope, Sly has his main door. It is the only shop in the Southern Rivers, but it is south of the main tunnel. Here is a menu of the Rangs Sly has in the full version.
Flare O Rang- This Rang emits a Flaming Ring around the target when hit. This Ring can burn the foe and is a match for the Mega Frills. It also does the exact things the Fire Rang does.
Ice O Rang- This one emits a ring of cold around it's target when touched. The ring freezes foes in their tracks and helps with medium and small foes. It copies some of the Freeze Rang abilities.
Thund O Rang- This Rang emits a shocking blast of electricity that can zap the foes with a present from above. The thunder stuns your foe and does a medium damage level and can use the Zap Rang abilities.
Omega Rang- This new Mega Rang has a Super Duper Seeker Camera in it that homes in on the foes and crates. It can keep your big brutes at bay while you think of a plan.
Matter Rang- The new Lash O Rang can not only spin foes under and grab Lash O Hooks, but it can grab Anti-Matter Crystals and slip through SOLID walls and STEEL fences.
Kabloom O Rang- The new Blast Rang can destroy steel crates and emit a large blast radius to break other stuff. Useful for when an ambush of Frills gets the drop on you.
Death Rang- This Rang is a curse to Cass when he made it. Sly's Rang is like a special Kabloom O Rang since it causes a gigundo explosion to kill Cass and his cronies.
Doom Rang- The most fearsome beast of all keeps it's name for a while, since it is awesome. It has a new RC feature to get the foe right away.
In Cass's Run, after you beat the Nano-Monster and Patchy, chop all of the trees in that arena down. Go to the 3rd yellow gate with a button above it, and shoot the button with a Mega Charge Boost from the Shadow Bunyip. A race to find the 4 triggers initiates, and these are the spots;
1ST- On the side of the building you entered, but the opposite end
2ND- right from the 1st one, but up high
3RD-On the rightmost waterfall, up high
4TH- left from the 1st one, but at the top
After you zap all 4, the yellow gate falls, letting you through. There are a few Cannonball Bunnies and a lot of Cass's Bunyips that can be killed right away with a Full Power Blast. At the peak of the mountain, there is a silver opal case with 10,000 opals inside. Since you can only get it here, come back every time to get it. If you are looking for opals for the Death Rang/ Doom Rang, you can go 3-8 times for 80,000 opals.