Defeating the Hell Mother is a bit easier than it may appear at first. When you make it out of the opening pool and through the teleporter, quickly collect all of the weapons. Defeat the shambler standing on Shub-Niggurath’s island in the middle of the lava. This will open the doorway up to the teleporter. It is possible, though difficult, to defeat all of the monsters headed your way. It is easier just to concentrate on the big lady herself.

Secret Area 1
When you reach the teleporter at the top of the path, look down into the pit. You’ll see a small ledge directly below you. Drop to the ledge and follow it around to a Quad Damage and a teleporter back to the main path.

Defeating Shub-Niggurath will take more than just a ton of ammo. Watch the spiked ball for a clue

Defeating Shub-Niggurath
Watch the pattern of the spiked ball. The position of the spiked ball indicates where you will appear when you enter the portal. Wait until it is passing through Shub-Niggurath, then dive in. You’ll telefrag the queen of evil and be treated to the anti-climax you should be used to by now. Congratulations.