Boss Brain (bb), is a .WAD created by Zombieguy/Cacodemon124.
and which it's also a sequel to "Never-Ending Icon 2/(nei 2)", During the game, You'll be in a starting area with Weapons and items just like from NEI...
There is also a door in front you which that means when you open it and walk through it, an Icon-like Wall will open up and there's also a Teleporter with candles on there.
This tells that there is going to be another Icon of Sin Fight Incoming!
When you teleport in, you'll be in the arena that has 4 Soulspheres (1 Invulnerability, On Easy...) and 2 Doors... one of them requires a "Red Skull Key" while the other door doesn't.
And also, during the arena. The Doors will open which will reveal the "ICON OF SIN" himself along with 2 Monster Spawners! so be prepared to fight.
Then when you open the Door 1# (Arena), You'll be in a blood room with the red skull key. But when you pick it up, more doors will open which will reveal 2 more Monster Spawners Which will make this game much Dangerous & Harder. (try not to get telefragged by the cubes of where they land...) Then after picking up that key, You will open the Door 2# (Arena) and you'll see the "BOSS BRAIN" (a.k.a, Romero Head, Icon Of Sin) and when you defeat him, The game will end... and you win!
Link: https://www.doomworld.com/idgames/levels/doom2/Ports/a-c/bb2
Thanks for listening in as always... ;)
Have fun and enjoy the Game!