Coil has worm-like form consisting of a square-shaped head at the front and the rest of its body being divided into square shaped increments the same size as its head and placed directly behind it. Coil's head is a purplish dark blue with two white eyes and a small purplish dark blue square placed at the back in the middle of its head.
Coil's body varies in length and, in contrast to its head, is made up of various shades of light blue that constantly flash and are lightest near its head and darker near its "tail". Extending from the square behind Coil's head, and spanning the length of its body, is a single line of a darkish light blue that ends at a small orange flashing square placed near the very end of Coil's body.
Coil starts each level 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 energy 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 is struck by a hazard, Coil will instantly die.
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|In the ending of Coil, a scientist is seen holding two cords and looking into a glass sphere that houses Coil. The scientist then plugs the two cords together and a white flash is seen and a picture of Earth covered in electricity, with Coil wrapped around it appears.|
- Bad Iceberg skin - A high resolution version of Coil appears in the water with a sad expression.