Our Xenoblade Chronicles guide features a comprehensive walkthrough and additional info on the endless amount of optional content in the game.
Walkthrough: Bionis Leg
If Colony 9 was large, The Bionis Knee/Leg is enormous. If you want to get right back to the story, head southeast towards the smoking wreck in the distance. If you want to explore the land, you can cover quite a bit of ground. There are some extremely high level monsters throughout the wilderness, even in places where the standard enemy is roughly level 12-14. In most cases, you can avoid combat by staying out of their line of sight and allowing them to pass by.
Shulk has a vision when he arrives at the wreck. The boy responsible for the vehicle seems to be in danger, somewhere near a body of water. Take off to the north in search of a water fall and a small lake along the edge of the map. You'll have to face off against two level 14 Berserk Ardun. This fight is simple if you don't make it too hard on yourself. Ignore the Monado's secondary skills. Focus on one Ardun at a time and try to inflict Break. This will allow Reyn to Topple the Ardun so you can beat it into submission.
Once they're done for, you need to escort Juju back to his home, a camp east of your location. To get there, head directly East from the Jabos Rock Rest Area, a landmark that should be on your map at this point. You'll run into some cliff faces adjacent to a group of trees. Follow the bend in the mountains, heading south. From there, the camp will lie just ahead.
Head into the camp and talk to the refugees if you are looking for quests, or stock up on new equipment if you've got some cash burning a hole in your pocket, but also know that the Gaur Plain offers plenty of opportunities to pick up special and unique grade items from battle. When you're ready to continue with the story, talk to Sharla to hear about the refugees escape from Colony 6.
Juju has run off again! Your goal is the bridge over Raquel Lake, located east from the camp. Make sure to stock up on new equipment. Sharla has two arts that will come in handy: Shield Bullet (Damage Immunity) and Cure Bullet (Debuff Immunity). Donít take them for granted. Unless you take control of Sharla or issue direction to the whole team, youíll have to wait for her to protect Shulk and Reyn.
When you arrive at the bridge, endure the cutscene and consider the available paths before continuing. You can head northeast and use the Windy Cave, but the less lethal route might Raquel Road, located on the same side you approached the bridge from. There are a few Mechon to contend with on the road, but the Windy Cave is littered with level 75-ish enemies that can only be avoided. If you donít want to risk restarting your trek, itís advised you take Raquel Road.
The tentacled Mechon that captured Juju is waiting for you at the goal. Heís at level 18, so itís advised to level up a bit if heís over your head. A good way to do this is by taking on side quests or exploring the map, both of which can and will keep you busy for hours. Bionisí Leg is massive.
Once you enter combat, the tactics required to win are fairly straight forward. First off, enchant Sharla and Reyn so they can actually inflict damage. Avoid using the Team Gauge to release a chain attack. Regardless of your efforts to enchant Reyn, or his ability to draw aggro, Shulk will likely be the primary target throughout the fight. Itís best to spend a little longer fighting the boss and reserve your team gauge for Shulkís revival, should he need it.
This fight lasts two rounds, followed by a third. Use the same tactics for the second round and since the third cannot be ďwonĒ, just attack as you please until the game takes control. Once your team decides to pursue the Mechon, head southeast from its location to reach your next destination, Bask Cave. Cross the body of water near the southern end of the map to reach the entrance.
There is an apparent mistake in Special Lever 2 for Regbuilding Colony 6.† It says defeat Earth Nebula at Sap Cave.† I was never able to find a Sap Cave, but I was able to defeat Caris Nebula at the brog lake just before you get to Nopon Arch.†