Creeper: They're lean, green and most definitely mean. While creepers have four tiny legs, they don't have arms, so they resemble snakes in appearance. Instead of slithering or crawling, however, they tend to "bounce" in the air.
They are also rather devious in their movement, since they often wait near your character rather than making a straight beeline toward you. When they are close, watch out: they will spontaneously combust after a little more than a second. You can escape the detonation simply by moving out of its range.