Now see, the pictures of the thing in this thread are actually cool and 'oh crap that thing is going to eat me'-inspiring. The thing actually comes across as a credible threat instead of something they came up with to shove in MM5 to fill space.
I got a lot of flak in the rpgnet thread for my selective immersion in D&D lore that's led me to not really care about demons and to have the name Demogorgon not even ring a bell like the names Orcus or Graz'zt or Pazuzu or what have you do, and dismissed as being a 'player, not a DM' who wouldn't buy or read MMs anyway. (I am in fact actually getting a 3.5 campaign together right now and in fact am currently reading the MM I bought ages ago, ironically)
Which... To my mind is a perfect example of why it probably isn't a good idea to put that thing, particularly that picture of it, on the cover of it.
If you're the kind of experienced grognard who does in fact read the monster manual for fun who's going to recognize that hey, that's Demogorgon on sight... You were probably going to buy it regardless.
If you're a hardcore constant DM who runs games all the time... You were probably going to buy it regardless.
If you're a new DM who's looking at books to buy who isn't intimately familiar with all the old demons... That weird thing on the cover is a two-headed baboon tentacle thing with all the awesome appeal of the flumph.
Though to be fair, seeing something that silly-looking on the cover, I'd probably look through it to see what the hells that goofy thing is and what other ludicrous stuff they'd put in the book.
Still, though. It does reek to the uninitiated of 'oh gods it's the jobber monster book'. Whether it is or not, and whether or not Demogorgon is a jobber monster or not, is irrelevant - If you don't know what it is, that thing looks freaking silly. If you DO know what it is, it still looks freaking silly.
