Frankensteiny

Frankensteiny (フランケンシユタイニー) is the second guardian ghost of Faust and is also his dead pet dog.

About
Frankenstieny is the pet dog of Faust and Eliza, who was with them ever since their marriage. Whilst never mentioned specifically, the dog apparently died a some point in the past - either due to the robber's attack, old age or other circumstances. It has ever since been with Faust in its skeleton form, constantly wandering with him. It made its first debut during the second round of the Shaman Fights where it was following Faust around, in his wheelchair. Later when Faust was attacked by the Icemen and they destroyed his wheelchair, he revealed that he used the bones of Frankenstieny as replacement for his missing legs, and that it can be completly revived with a little amount of Furyoku and give Faust great jumping power.

O.S. Frankensteiny
O.S. Frankenstieny

Description: After giving up his lower legs to Eliza, Faust was confined to a wheelchair and became unable to walk for the rest of his life. However after training with Kyōyama Anna he learned how to oversoul the bones of his dead dog into a pair of legs.
 * Shaman:Johann George Faust VIII
 * O.S. Type: Spirit Type
 * Spirit Ally: Frankensteiny
 * Medium Used: Skeleton Remains of Frankensteiny

This is done by splitting the bones up in the middle of the spine, so that the front legs are attached to his left leg and the back legs are attached to his right leg, both of them being attached with the spine. When first shown this seemed to put some restrain on the bones, but has not been adressed since.

Anime/Manga Difference
In the anime, Faust never loses his legs to Eliza, and Frankenstieny is never seen walking around, so therefore is he only seen briefly in a flashback in episode 15.

Trivia

 * His name is play of the word Frankenstein, a mad doctor who stitched together corpses and reanimated them with the power of lightning.