If you see a strange winged being resembling a crow and a wyvern, you have encountered a Crowern. No doubt their origins lie in some dark laboratory experiment. Crowerns are strong and very aggressive and they use flight and speed to their advantage in combat. There may be evolved forms of Crowerns deeper in the dungeons.
A ghastly experiment gone awry, Crowerns were released into Grimrock many years ago, and have since bred themselves to a respectable number. While they are prey for some of the monsters on the lower levels, on most of the upper ones, their ability to fly means they reign supreme. However, with only snails to eat, they've grown hungry for fresh meat, and thus, very aggressive, ready to attack the first adventurer they see! Some have even gotten too close to portals, and in a strange mutation, have gained the ability to fire bolts of electricity. It's wise to avoid these creatures, if you can.