Kameo: Elements of Power

Turn into Pummel Weed. Use the weed creeper attack that involves pulling both the LT and RT button at the same time and find an explosive shell on the ground. While under the ground, inhabit the shell with the LT button, just like you did when you had to break down the gates earlier in the level. While controlling the shell, head to the tree while avoiding his attacks (they're pretty slow, its pretty easy). When you get close to the tree, pull the RT button, making your character upper cut the explosive shell into the tree. He will wobble a bit and then spit out trolls from his branches. While he does this, turn into Rubble. As you are fighting the trolls, the tree doesn't attack much, but instead starts to laugh and opens his mouth really wide. While he does this, use the stone chip attack (LT) and throw rocks into his mouth. Repeat the process until the tree is beaten.