Coil is an electric snake with a square-shaped, purplish dark blue head, two white eyes and light blue square-shaped increments placed behind its head. Each level begins with Coil in four block increments that can be destroyed upon contact with hazards or made longer by contact from energy blocks. Coil's body can conduct electricity if it is touching a power generator or a similar energy producing object whereupon contact with any other object will cause it to conduct electricity as well. If Coil's head comes in contact with a hazard, Coil will instantly die.
Coil's true intentions are revealed once the 16th level is completed. After looking into a glass sphere that houses Coil, a scientist plugs two cords he is holding together and a white flash is seen. A picture of Earth covered in electricity with Coil wrapped around it is then shown, ending the game.
A high resolution version of Coil is shown in "Bad Iceberg" skin. This version of the character is seen in the water with a sad expression.