E4M8: The Crawling Chaos (Strange Aeons)

E4M8: The Crawling Chaos is the fourth boss map of Strange Aeons, designed by Impie in 2015 and constructed in Doom Builder 2.

Essentials
The nearby door opens via the switch on the platform in front of you. You can open the door and go straight to the fight, or take the detour to the left of the switch for extra goodies.

The detour leads to a mob of Devils and a Leng Spider ambush, but rewards you with an AK47, plenty of ammunition, and a couple of secret powerups (Rage Sphere, Blue Armor, Medikit).

Beyond the door, Spiderbabies stand guard over a Soul Sphere and the slipgate to their master's lair. When you're ready to fight, jump through the slipgate.

Avoid fighting Nyarlathotep and focus on the monsters on the four platforms with the white pillars of light: they're the ones who summoned him to Leng. Each time you kill one, the light goes out and stops emitting eerie ambiance. When all four lights have gone out, Nyarlathotep is bloodily banished from the realm, and the exit slipgate opens, allowing you to return to Earth at last.

Boss: The High Priest Not To Be Described
To escape Leng you must defeat one of Nyarlathotep's nightmarish avatars. The flying Elder God bombards you with swarms of wraiths, volleys of magic missiles, and trails of fire that chase you down like blood hounds. Worst of all he ducks, weaves, and teleports constantly: most of the time, only a lucky shot will hit him. It is possible, however difficult, to stun-lock him with a Rage Sphere and Yithian Lightning Gun. Killing his minions is the easier route.

Secrets
Halfway between the starting point and the Devil camp is a secret wall concealing a Rage Sphere.

A somewhat hard-to-see staircase leads up to the cliffs surrounding the Devil camp, where you will find a Blue Armor. Grabbing it lowers the cliff and unleashes a Leng Spider ambush (plus a cache of bullets).