The problem for me comes in the suspension of disbelief, here's the red dragon, voracious, vicious, lethal, and unless you're a hobbit with script immunity, will quickly turn you into crunchy soup... In the monster manual you can see it as clear as day, surely that removes something of the mystery involved in the game? How many adventurers have actually seen a red dragon, how many adventurers have lived to tell the tale, surely creatures like this shouldn't be obvious to everyone, surely only a few should know what one of these things looks like...
I always liked the idea that the creature wasn't in the monster manual, that it was something that no other adventurer had ever seen, and it's that that I'm working on for Quest. Creatures come in three different classifications, Green, Red, and Black, as gauged by the exploration guild.
Greens are mostly harmless, not likely to attack, and as such have most of the detail in them, creatures such as the Ceverill.
Reds on the other hand aren't immediately dangerous, but will attack if provoked and are far more dangerous to encounter, you can still get a good drawing of them if you're not too close, creatures such as the Burle.
And finally, a creature classified as Black is dangerous in the most extreme, they attack on sight, are extremely territorial and very dangerous, creatures such as the Cheni.
And the Carenan Devils
I haven't had them properly laid out yet, but I'm interested to hear everyone elses thoughts on the mystery of creatures in RPGs