Coffin

Coffins (棺桶) refer to large quadrupedal robots controlled by the corpses inside, specifically that of an esper. Coffins are able to boost the powers of the espers inside them and are able to use them to great effect.

First introduced in Toaru Kagaku no Accelerator, they are manufactured and used by the DA to cleanse Academy City of "evil".

Principles
The Coffins uses "evil spirits" of the numbers to allow it to function. It is currently unknown what these are.

The mecha can strengthen the abilities of the espers inside of it based on their level, in fact it can even boost it to a Level 5 ability. The mecha or the corpse inside of it can somehow follow orders and is intelligent enough to rescue its allies.

Prototype
The first seen Coffin is the Prototype. It is large quadruped mecha, with one large sphere that acts as the eye and is where the corpse of Hitokawa Hasami. The mecha has two tentacle-like appendages on of its side. It has powerful legs and is able to leap from a large fissure.

Using Hasami's ability, Pyrokinesis, it can boost her Level 2 ability to that of a Level 4.

Qiong Qi
The Qiong Qi (窮奇) is a large Coffin that uses a strengthened Psychokinesis ability equivalent of a Level 5. Unlike the more machine-like Prototype, the Qiong Qi is much more streamlined and animal-like in appearance. It has a head where its eyes are located, four legs, and two arm-like projections on its sides.

It is very powerful, able to dissipate Accelerator's wind attacks. It is used to kill Nishio, mutilating his body and even melting his flesh. Similarly to the Prototype, it can make powerful leaps up to the sky.

Others

 * Taotie (饕餮)
 * Hudun (混沌)

Trivia

 * Qiong Qi, Hundun, and Taotie are mythical Chinese creatures as mentioned in the in the Shanhaijing. They are three of the Four Fiends in the book.