Skele is a nick-name for one of the monsters in-game. Skele is clearly different from others, with full body showing and no teeth. Skele is the most dangerous and mysterious out of the 5 total monsters.
It seems that Skele is a skeleton version of the other monsters. Skele has a very empty skeleton and eyes that seem to stare. In the second game, Skele has no eyes, but eye sockets showing out (in the picture on the left).
Skele usually has parts of his skin around his feet, and most likely shows that his skin has fallen off over the years.
In ESCaPE 2, however, Skele looks almost completely different, and has visible eye sockets. An image from a preview for ESCaPE 2 (That was shown publicly on Dec 18th, 2014) shows Skele staring at you, with the words "He is back" repeating over and over (referring to Skele in the first game) until it says "You are back" and continues in the background. Skele has no eyes like last time, but now the eye sockets are visible, and show a black dot in both eye sockets.
Behavior EditSkele's behavior is similar to all the other monsters in the first game, but in ESCaPE 2, Skele has increased speed compared to the other monsters.
Since Skele's speed is so fast, The creator added a sign to know when Skele is near you. Skele emits a sound in-game that sounds like static, glitching and somebody with a very deep voice mumbling. The sound increases in volume when Skele gets closer to you.
Skele's jump-scare is very different from the others, though. Instead of leaping at you with it's arms in a T shape, Skele emits a very different scream and thrusts it's head back and fourth with a glitching effect.