The Underworld consists of, for the most part, several "islands" that you must make your way across by finding and pressing several buttons that are found under very obvious rocks. It is not very hard to get lost in this level. However, it is easy to get overrun by enemies, since each island has two, three or more purple ground generators. Once you reach the island with the golem, you are right at Skorne's front door. Once you kill the enemies and press the switches on the island, it is time to face Skorne for the final time.
Final battle with Skorne
Some of his attacks are different this time. He shoots fireballs from both hands, breaths fire, shoots a very powerful beam of what looks like a golden light from his chest, shoots spikes from his chest and creates a round beam to knock you over. The best strategy is to run around avoiding his attacks until he takes a short break or he shoots his flame breath or chest beam. If you decide to attack during his breath and chest attacks, you have very little time to get out of the way, position and fire. If you continue avoiding his attacks and striking him with your own, he will fall.
When you do make Skorne fall, you will return to the main area of the game and Sumner will give you a very special reward.