Old Dungeons and Dragons, most games of that nature in fact, take a lot of their beasties from traditional mythology. The crazy is when you take something from a fairie tale and put it into an ecology. Now take the cockatrice (please!) In the myth, the cockatrice was deadly poison. So poisonous that if you ran it through with a lance the poison would run up the lance, kill the knight, THEN kill the horse. It was so deadly that soon the area around would be reduced to nothing but barren waste.
Now in the old D&D (I haven't picked through the new stuff) they changed it a little. In the D&D world the cockatrice merely turned someone to stone with a touch (and a failed saving roll, but let's not get into saving rolls that way lies madness I tells ya). Also, they decided that the cockatrice was an uncommon monster.
Did anyone ever think what this meant? We have something that's basically a scaley chicken that is turning everything into stone. Worse, there most be quite a few of them if they are something that is not a rare or a unique beastie but rather uncommon. It's basically using their stats about the same chance as meeting a mountain lion. What isn't being turned to stone? Is the world just full of statuary?
Well, on second thought it might not be so crazy a situation. Of course the cockatrice would be uncommon when you think about it. Turning things to stone must be a hell of a defense mechanism. What's going to be the natural prey of a cockatrice? Even diseases aren't going to do much. They must be continually shedding a light dust of bacteria. The question would be, is the cockatrice a predator or the type of creature that is going to go out of its way to turn everything to stone? It could be a rather peaceful and retiring creature. Nesting in stony once trees and pecking on petrified berries (it would have to be ingesting stone even if it was turning it back into flesh once in its belly). This cockatrice would be something that the farmer might see in the distance but not a monster that is flying out attacking everyone. No doubt the lore would be, if you see a cockatrice very carefully and SLOWLY back away and don't upset it. They would still be doing vast ecological damage to the environment turning trees and such to stone but at least it would be no worse than say an infestation of gypsy moths.