The Trollface level was super secret level-intended even in Tristania3D

The game had 2 different floating ghost enemies, and I only wanted to use one, so I was left with an unused enemy type - this is where Trollface/Coolface came into the picture. And later, mah ver' good friend insisted that we should put in Hello Kitty instead of Trollface. And so it happened.
The Dopefish idea was meant to be an Easter-Egg, as it is not a meme or anything

Besides, every good game has at least 1 Easter-Egg hidden inside (Tristania3D has the Hello Kitty for instance).
I can create some advertisements as well, but beware - they shall be 24Bit PNGs, not simpler ones like these (mostly I selected these billboards, because their quality would not be distorted when imported inside Doom). Non-commercial advertisements and billboards of course. So if the 24bit is not a problem, I'll create some advertisements for you, apart from the Tristania3D one
The NEDM fits perfectly for a billboard in Doom - basically it's a phrase for cruelty against animals is bad, that's why I would use it.
Main problem is, my advertisements are all in Hungarian

it'll take time to re-create'em in English, but of course it's far from impossible. What should be the maximum size, so you don't need to resize anythin'?