Avoid all slams of the big Totum Hokum Boss. When he opens his mouth, you will see sonic beams. You do not have to be careful about them because they will not harm you. When he opens his mouth, throw Cortex in it. Repeat this a few times to defeat him.
At first, the boss uses punches in the ground that create small shockwaves. Just run in a circle to avoid them. He also may dig slightly into the ground and try to hit you from underneath with one of his arms. When he starts breathing in, throw Cortex into his mouth, kill the tiny golems as necessary, then grab Cortex when he gets spat back out. The second attack pattern adds laser beams that shoot from his eyes. Repeat the first step with throwing Cotex in his mouth. More small golems will pop up this time, and you may need to hit and run. The third attack pattern is the same as the second, except a large number of small golems pop up when you throw Cortex in his mouth. Because this is his last life, just run from the golems. The totem God will spit Cortex back out and you will have won.