Arch Behemoths are enemies exclusive to Kingdom Hearts: Final Mix.
Arch Behemoths are blue variants of Behemoths, replacing the Behemoths from Kingdom Hearts in End of the World. They are no different than the Behemoths in the same area in Kingdom Hearts. On another note, their color scheme resembles Hades.
In Kingdom Hearts II
Two Arch Behemoths are shown in the Battle of 1000 Heartless though they can not be fought.