Horse Grimm

Horse Grimm (unofficial) are large, horse-like Creatures of Grimm from the American animated webseries RWBY. Only one has appeared in the series thus far, fused with an Imp to become the Nuckelavee Grimm.

History
Horse Grimm, like all Grimm, were created by the God of Darkness to offset his brother's creations. After the Grimm fell under the control of Salem, she mutated and combined Grimm, including one Horse Grimm that she combined with an Imp to create the Nuckelavee, which later attacked the town of Kuroyuri, destroying it beyond repair and killing most of the citizens living there; including Lie Ren's parents.

Volume 4
In "Remembrance", Team RNJR comes across the ruined town of Shion, which has been attacked and destroyed by the Nuckelavee Grimm. Ren and Nora notice the creature's footprint in the dirt, but decide to say nothing.

In "Two Steps Forward, Two Steps Back", Ruby and Jaune take Qrow down the path to the ruined town of Kuroyuri, unaware of the Nuckelavee Grimm's footprint beneath them.

In "Kuroyuri", Ren and Nora discover a cave where the Nuckelavee Grimm has been living and leaving behind tokens of its conquests. Upon looking out the other side, they see the trees ruffling as the Nuckelavee Grimm roars and makes its way toward Kuroyuri.

In "Taking Control", the Nuckelavee Grimm arrives at Kuroyuri, roaring as it spots Team RNJR.

In "No Safe Haven", the Nuckelavee Grimm battles Team RNJR, overpowering them with ease. Ren attempts to attack it and gets pinned by the Grimm, forcing Nora to save him but getting beaten and depleted of Aura in the process. Ren breaks free and charges the creature again in a blind rage, but is also defeated and depleted of Aura. Ren soon comes to his senses after some words from Nora and together Team RNJR devises a plan to defeat the Grimm; pinning the humanoid portions arms to the ground while Nora kills the equine portion with Magnhild. Ren then severs the humanoid portions limbs before decapitating it, killing the Grimm and avenging his parents as well as everyone the creature has slain.

Powers and Abilities
As shown by the Nuckelavee Grimm, Horse Grimm are extremely fast on their hooves. They are also incredibly strong and durable, able to take powerful and multiple hits and sustain barely any damage.

Trivia

 * The Nuckelavee Grimm was confirmed to be a fusion of an Imp and Horse Grimm in the Volume 4 Crew Commentary.