This is a VERY unique fight, trust me. The Obsi legs are not the main opponent, the HUUUUUGE one in the background known as Titan Legs is. We need to wait for boulders to fall into the scene, so we can chuck them at the Release buttons, releasing more lava into the area. Hit all 3 and Titan Legs will be incinerated! Remember the rules, they're in Ep. 1!
What now?