Go to the creeper and he says: ,,Zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz...........................!"
And he explored you. He spawn in caves or in the night. This is TNT in a NPC. He haven't arms, but for legs. He drops gun polwer. If you have enough gun polwer and sand you can make TNT and explore NPC's. If lightning strickes a creeper he have an very big explosion.