Map15: Obscure Base Part III: Rocks and Stones (Prodoomer)

This large and circuitous level introduces the Plasma GEL plasma gun and a deadly miniboss type enemy called a scourge, which the player must fight almost immediately. Since it has two hitscan attacks that can take off most of the player's health easily, it is best to stay out of its line of sight entirely and use indirect attacks.

The red skull switch room offers a good opportunity to dispatch the high level imps by casting Blizzard, Telekinesis, or Rays into the pillars.

When swimming through the mine-laden waters to reach the blue keycard, the player can destroy the sea mines both by casting Sandbags at them and casting Telekinesis in their direction. The deeper the player is in the water, the more effective the latter will be. Be aware that yes, it is possible to drown if the player stays down too long.

Towards the end of the level is a long elevator leading up to a control room and hangar, where a horde of tough enemies, including another scourge, is waiting in ambush. Stay at the bottom of the elevator shaft and use Tornadoes, Blizzard, Electric Bow, or any other indirect attacks to clear out the room ahead of time.

Average Payout: 4,700 credits

Secrets
1. On the west side of the first outdoor area is a false wall. Crouch to get through and collect the treasure.

2. In the room with the red skull switch and eight pillars with imps, search the south wall on the east side for a secret.

3. After reaching the base on the eastern side of the map (guarded by zombies and cacodemons) take the elevator up the tower and get onto the perimeter ledge. Check the west side for a hole, drop in, and find some ammo.

4. In the room near the end of the level with the arch-viles in the center, check the northeast corner at the top of the stairs for a secret door. To get inside and collect the armor, double jump and then crouch.

5. After clearing out said room and pressing both switches, go back down the elevator, kill the kamikaze that comes out, and check the area it was hiding for some treasure.

6. Backtrack a little more to find a secret compartment to the west has opened. Get the ammo.

Secret Item
Come back to this stage with the Remote Control upgrade for the Rocket Launcher. Go to the lake that leads to the underground river where the blue keycard is located, and rocket jump onto the high ledge. Check the automap and examine the south wall for a small gap in the border line to the left of the underground river. A false wall section is visible near the top. The player cannot actually rocket jump into this corridor, but projectiles can still pass through. The player will have to fire a guided rocket into the hole and carefully steer it through several miles of twisted tunnels to strike the target at the end, eliciting a bass guitar riff upon successful completion. This will open a secret area in the starting area of the level, revealing an upgrade. Note that it's possible to save and load the game while piloting the rocket, in case the player makes a mistake.

To earn the achievement "Badass Combo" the player must then land 100 punches in quick succession. Since it can be difficult to get monsters to hold still, the easiest way is to punch one of the invulnerable marines stationed in The City.

Rings
30 After opening the exit path to the level, go back to the watery underground area near the beginning containing the ambush of high level zombies. The compartment at the top of the stone stairs to the east (where there was a lost soul) will have opened, revealing the ring.