You've reached the last stage of the episode. You begin in what appears to be a small room with no roof. Hit the switch: the floor will rise up, revealing that you were in a shallow pit on the edge of a large outdoor area. You'll see gaps on either end of the curving section of wall ahead of you, allowing glimpses into what looks like another large area beyond.
First, lots of enemies
You can go either left or right from this area. Follow either route, and you'll see that you're going around the perimeter of a very large central area. Circle the entire area and clear out all the enemies. There will be lots of ammo and items available. At one point you'll come to a stairway that looks like it goes over the inner wall and into the central area. It does, and that will be your eventual destination, but before you do, there are a couple of bonus areas you'll want to see. At the east and west ends of the level, look for small curved sections of wall along the outer wall. Behind each one there's a door that might not yet be open. For the east side, go around the corner to the depression and pool, and step onto the mound where the Inferno Orb and Dragon Claw are. This will open the door. When you go inside here, a series of columns will begin to raise and lower. Just run past these and to the far side, where you'll find Wings of Wrath, items and ammo. Activate the wall with the gold symbol: inside here is a teleporter that goes back to the other side of the moving columns. To open the west-side door, step onto the nearby mound where the Ethereal Crossbow is. Inside is a small room, where you'll find more Wings of Wrath, a Mystic Urn, armor and ammo. (The back wall with the gold symbol looks like a hidden door, but isn't.)
At this time you're ready for the final showdown. Go up the stairway to the central area. On top, between the stairways, you'll find a Mystic Urn. When you go down and inside, the two sections of wall that had the gaps will lower, allowing easier access from now on. You'll be promptly introduced to this level's resident Bad Guy, the Maulotaur. These bovine-looking baddies have several modes of attack and take a beating. Two Maulotaurs serve as boss enemies in this level, but they'll occasionally appear again in subsequent episodes. Probably the most efficient way to fight them is to activate a Ring of Invincibility and a Tome of Power, and use your Phoenix Rod. When enhanced by the Tome of Power, the Phoenix Rod will become a sort of flamethrower, with each round lasting up to about ten seconds with sustained triggering. If you can consistently keep the flame on the Maulotaur, it'll be toast within two rounds. This can be difficult because they charge and ram you. When they do, don't stop firing while you reacquire them and you'll save your ammo.
Before fighting the Maulotaurs, run to the structure in the middle of the pool, where you'll find a Ring of Invincibility. Also, look behind the lowered section of wall nearest where you began the level. You'll find still more Wings of Wrath next to that inner section of wall. Surrounding the pool are four teleporters inside frames, each of which just leads somewhere outside, but will allow you to quickly get away if things get out of hand. There are also items (Phoenix Rod, Morph Ovum, etc.) in the middle of the teleporters, that you'll pick up when you step into them. (If you teleported but didn't pick up the item, run into the teleporter from the side facing the pool.) You'll also see four more frames with the insides covered up by wooden panels.
Go to work on the Maulotaurs. With the enormous quantity of ammo, health and items available, probably the biggest risk is having a powerup unexpectedly expire on you or losing track of your health. If you're not using Rings of Invincibility, using Wings of Wrath will allow you to avoid the trails of fire they shoot along the ground. And, like with any group of enemies, try to fight them one at a time, that way you'll have both of them beating on you only until the first is defeated, rather than for the entire battle.
When you've defeated both of them, the wooden panels inside those four frames will lower, revealing exit portals. You've now completed the episode. Step into any of the exit portals and enjoy the ending sequence. Although the game is now over, it'll assume you'll be beginning a new game with the third episode, The Dome of D'Sparil.