I can't find a map I'm searching for

Hi

I remember playing a megawad with a map where you walked up to the gatekeeper and his mouth opened. Inside of the gatekeeper there where lots of barons and hell knights along with the sksnake texture.

Wich wad is it? And what map number?

Thanks

BIOWAR MAP18. Also the best execution of the boss brain I've ever seen ('cept maybe Plutonia II).

For another giant mouth boss, the end of map 34 (needs -warp 34 in start/run) here has a big lamely drawn retard /spam
http://www.doomworld.com/idgames/index.php?id=15982

thank you very much!