The Arc Behemoth is an Emblem Heartless that is found in Kingdom Hearts Final Mix.
It is a blue version of the original Behemoth, and has a flame design marked onto its body. Arc Behemoths appear multiple times throughout End of the World, although they aren't as strong as a normal Behemoth. In the original Kingdom Hearts, normal Behemoths occupied the area instead, but this was changed, with the Arc Behemoth receiving its own entry in Jiminy's Journal.
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 are based on the Behemoths found in the Final Fantasy series. These Behemoths are also large, horned creatures with massive strength. "Arc" can refer to an electric arc, a discharge of electricity between two points.
At the start of the battle, they will most likely begin with loading up the orb that it launches in the sky. If you want to avoid getting hit by the orbs that fall down, try to sneak under it after it has launched the orbs in the sky. After that, you'll want to focus on getting on its back and repeatedly attacking its horn. If it is stunned, do about two combos and then back away, for it will cast Lightning that will hurt a lot. If you get away from it, this will miss. Keep doing this and eventually you'll beat it. Cast Aero if you can't avoid getting hit.