Newtron (メレオン Mereon?) is a chameleon-type Badnik created by Dr. Eggman. It makes its first appearance in original 16-bit version of Sonic the Hedgehog. There usually exist two types in the games, as both types of Newtrons are one of a handful of Badniks which exhibit a cloaking ability.
Newtron as a Badnik is based on a chameleon. A Newtron's body has a head, stripy tail and four white feet, and each of the feet have three fingers. One of the fingers stretches in the other direction, so the Newtron can hold extract. A Newtron has yellow photoreceptor eyes with small pupils (later colored cyan), and a brown sharp parietal crest. Newtrons come in two varieties: green and blue. The green variation has yellow eyes and the blue has red eyes, though in Sonic Generations, both variations have cyan eyes.
Newtron's design in Sonic the Hedgehog 4 is more detailed. In Sonic Generations, Newtron is more mechanical in appearance and both varieties have cyan eyes. In Sonic Lost World, Newtron is given a softer appearance.
Both green and blue varieties hide camouflaged inside a wall and phase out of hiding when they see Sonic, but they have different methods of attack:
The green Newtron, after becoming visible, aims at Sonic with a built-in E-5s laser sniper rifle in its mouth and fires. It then phases back into its surroundings. It never moves outside of its wall and most are out of reach , so most of them are technically invincible.
The blue Newtron doesn't stay in one place or try to snipe Sonic. After becoming visible, it jumps off the wall and morphs into a chameleon-shaped rocket, which chases Sonic in a fixed horizontal line at a fast pace. The blue variety is easier to deal with as it can be attacked, unlike most of its green counterpart units. Green Newtrons in Sonic the Hedgehog 4: Episode I however, are also able turn into rockets as well.