The Arc Behemoth can be found exclusively as a boss in Kingdom Hearts Final Mix.
The Arc Behemoth has a massive body, with a huge barrel-like chest that tapers into its back end. The Heartless Emblem is located on the underside of its chest. Its coloration is a dark grey-blue on the underside of its body, with a light blue on top in the design of flames. These flames extend to its shoulders of its large front legs, which are much larger than its back legs. A very light blue decorates its forearms, and the feet are black with more flames extending onto the forearms.
Its four feet all have a circular pad on the bottom, with two inwardly facing claws on the front. Its back legs are shorter, but boast the same color pattern as the front legs, with the black of the feet extending all the way up to the knee. The Arc Behemoth’s mouth is jagged and extends outwards into two large inwardly curving tusks, which are colored black. The forehead is flat and the eyes sit facing forward, and glow yellow like the other Heartless. A conical, grey horn sits at the top of the head, facing forward at a slight angle.
The Arc Behemoth's name and design is based on its appearance in the Final Fantasy series; Behemoths are large, horned creatures with massive strength. When "Arch" is used as a prefix, it usually means that the subject is highly placed in a hierarchy. This contradicts the Heartless's weaker strength when compared to the original Behemoth.