The Arch 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. Arch 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 Arch Behemoth receiving its own entry in Jiminy's Journal.
The Arch 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 Arch 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 Arch 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.
At the start of the battle, they will most likely begin with loading up the orb that it launches in the sky. To avoid getting hit by the falling orbs, try to sneak under it after it has launched the orbs in the sky. After that, focus on getting on its back and repeatedly attacking its horn. If it is stunned, do about two combos and then back away, as it casts Lightning which deals a lot of damage. Keep doing this and eventually it will fall. Cast Aero if avoiding its attacks proves difficult.