Map 2: Underhalls

Start by defeating the Zombiemen in front of you and entering the door.

Clear enemies inside and find the switch on the left. This opens the waterway near the entrance to the east.

Head back and follow the waterway. Be cautious of alcoves with hit-scanners.

Proceed east through the door. This room is filled with hit-scan enemies; use corners for cover.

At the end of this room, you will find the SUPER SHOTGUN. Note that it uses two shotgun shells per shot and is excellent for tougher enemies.

Return to the waterway and continue. To the left, you'll see a building. Clear enemies inside and around it, including those in a window.

Inside the building, you will find the Red Key Card.

There is a secret area: facing left while looking at the key inside the building, interact with the wall to open a door to the area where gunners were in the window. This is [SECRET 1/1], rewarding you with ammo and Mega Armor.

Grab the Red Key Card.

Use the Red Key to open two monster closets: one to your right with Imps and a Pinky, and one to your left with hit-scan enemies. Both contain health.

Head back to the entrance and through the door that was previously barred. Hit the switch here to open the waterway leading west.

Follow the waterway west, clearing enemies. It leads back towards the building area.

Explore the southern room. This area has two ground-level rooms filled with enemies, including Pinkies. Fire down into the rooms to thin out enemies before dropping in. Use barrels strategically.

Drop into the rooms and use your Super Shotgun to clear the remaining enemies.

Find the Blue Key Card in these lower rooms.

The Blue Key Card opens a door on the western portion of the waterway, containing several Shotgunner enemies. This is the Level Exit. Ensure you have 100% items and kills before exiting.