Segomo is the final planet. It's relatively straight forward but the boss is a little different.
With out spoiling it, the boss fight is a little strange. You are looking for silver objects that look like satellites at your height. They have red lights on them that have to be destroyed. You can either shoot them (with fire or ice for the best results) or use a bomb. When you destroy all the red spots (which happens instantly with a bomb) the boss's life will go down by quite a bit.
After a short while (less than thirty seconds) another satellite will spawn.
While you're doing this, other enemies and items will spawn, deal with them as you want. The fastest way to through the boss battle is to hang on to three bombs, but it can be done quite easily with just normal weapons.