Caterkiller

Caterkiller, also spelled Catakiller and known as "Nal" (ナール Nāru) in Japan, was a first-generation Badnik created by Dr. Robotnik in the original Sonic the Hedgehog.

Catakiller seems to be a favorite design of Eggman, since it is re-used in many other forms. For example, a modification of it, called Sandworm, appeared in Sonic & Knuckles in the first act of the Sandopolis Zone.

Appearance
The Caterkiller model is based on a real-life caterpillar, both in its shape and the way it moves across the ground, stretching its four segmented body parts up and down to crawl along its programmed territory. It has two antennae located at the tip of its head. An interesting feature of this Badnik is its ability to separate its four body parts if one of its 3 spiked segments are hit. As long as the head remains intact, this Badnik will continue to survive, albeit scattered throughout the area. Teeth can be seen on the front of the Caterkiller, but they have never been documented to have attacked with these. Standard colors for the Caterkiller model were a purple body shell with a gray underside, with a smattering of yellow for the antennae and spikes.

Attack Pattern
The Caterkiller's main attack pattern lies in its ability to only have one segment that can be destroyed without any injury to the attacker, making it more of a defensive Badnik than an offensive one. As stated in the Physical Appearance section above, not only will the attacker be hurt if they try to hurt the last three segments, but the segments will detach and scurry around the area, causing even more potential damage. Sonic had to be extremely careful when dispatching these enemies. The Caterkiller will also sometimes turn, but it is possible to hit without taking damage/losing a shield when Sonic is not invincible.

To defeat one, Sonic must do a Spin Dash, Spin Jump, or roll into/onto its head, otherwise Sonic will take damage, and will scatter the Caterkiller's segments all over the place. If you destroy a Caterkiller this way, a creature will not be freed.

Sonic the Hedgehog
Catakiller appears at Marble Zone and Scrap Brain Zone in 16-bit version of Sonic the Hedgehog. In 8-bit version of the game he only appears at Scrap Brain Zone.

Sonic 3D
An unnamed caterpillar robot with the same appearance also appears in Sonic 3D in Green Grove Zone Act 2, leaping between holes in the ground.

Sonic Jump
The original Catakiller haven't make appearance until at Mountain Zone in the 2012 remake of Sonic Jump.

Different Versions
The Caterkiller is the precursor to the third-generation Catakiller Jr. (known as Meramora in Japan), which has the added ability to hover and protects its body with an energy wave.

Crawlton from Sonic the Hedgehog 2 is similar in design, almost an 'upgrade' of Caterkiller. It appears in the Mystic Cave Zone, like Sandworm after it, it is blue and yellow rather than purple and yellow.

Sandworm from Sonic & Knuckles greatly resembles the original Caterkiller, although it is blue instead of purple. It does not crawl, instead burrowing through quicksand, and can even leap out of the sand to attack the player. In Japan, both Caterkiller and Sandworm are known as Nal making them the same Badnik.

In Sonic the Hedgehog CD, an enemy named Kemusi is similar to Caterkiller.

In Knuckles Chaotix, an unnamed enemy in Botanic Base Botanic Base Badnik 2 is an analogue to Caterkiller.

Sonic the Hedgehog Story Comic
Caterkiller appears in Sonic the Hedgehog Story Comic manga. At the beginning of Sonic the Hedgehog Story Comic Volume 2' story ''Clash!! South Island'', Caterkiller chases Pocky at Marble Zone until Sonic destroys it with with a his Spin Attack and saves Pocky. Little later Picky emerges from the wreckage of the Caterkiller, being as a organic battery of the Badnik.

Sonic the Comic
Caterkiller badniks appeared in early issues of Sonic the Comic.

Archie Comics
Caterkiller badnik have also been appear in early issues of the Sonic the Hedgehog series from Archie Comics.

In Archie Sonic #119, a giant train-like Caterkiller was sent to overrun Furville, but Sonic the Hedgehog and Miles "Tails" Prower managed to put it to a stop.

Trivia

 * Caterkiller was originally intended to appear in the Spring Yard Zone instead of the Marble Zone, but was switched with Spikes late in development. Caterkiller appears as a default badnik of the Spring Yard Zone in Sonic 1's debug mode.
 * Caterkiller was the first Badnik Sonic encountered in the Archie Comics instead of Moto Bug.
 * Crawlton, a Sonic 2 badnik, appears in Sonic the Hedgehog: The Movie. In the movie this badnik bears a pink color-scheme as Caterkiller but in Sonic 2 Crawlton originally had a dark blue appearance. This could be character design error in the film.
 * In Mega Man X3 there is also an enemy named caterkiller. However there is no resemblence.