Minecraft (Pocket Edition)
Creepers spawn where light levels are too low or when it becomes night. They are also sometimes found in Dungeons as the result of a Creeper Spawner.
Usage / Purpose
Other than their drops of Gunpowder they are essentially just an unattractive nuisance.
Drops / Yields
Creepers are available in both Survival Mode (as a naturally spawning creature), or in Creative Mode as a Spawn Creeper Egg.
Each time a Creeper is hit it shudders and makes a burning-fuse sound. If the Creeper does this for a prolonged period of time it will explode. If you hit a Creeper with an object or Sword it is a good idea to strike and back off to allow the Creeper to defuse a bit before striking again.
The above image is an example of an explosion hole after a Creeper detonated.
The Creepers' likeness is immortalized on the Sandstone Chiseled block, if you didn't already grow weary of staring at its nasty face.