The quickest and easiest method of defeating Humbaba involves using Energy along with Dualcast and either SP Turbo/Turbo Magic/Master. If Zack has the maximum MAG stat of 255 (or thereabouts), then using the above strategy, Humbaba can be defeated easily in one shot. The use of Energy is especially useful when facing against larger monsters such as Behemoth and its counterparts (e.g. Behemoth King, Sea Hulk, Jabberwock, etc), because the number of hits increases proportionate to the size of the monster. One casting of Energy at a Behemoth-type monster will therefore yield several hits as it "passes through" the entire length of the monster's body. Use in conjunction with Dualcast for maximum effect. If a single SP Turbo materia is insufficient, then you can also equip SP Turbo Magic and SP Master as the effects are stackable for even more damage. Usually equipping two will result in the maximum damage of 99999.
To make things easier Graviga can be used to lower his HP to a more reasonable amount if Zack's MAG is low, but multiple castings of Energy is usually far more effective.
Humbaba (Assyrian spelling) or Huwawa (Babylonian) was a monstrous giant of immemorial age raised by Utu, the Sun. Humbaba/Huwawa was also the guardian of the Cedar Forest where the gods lived. In the Epic of Gilgamesh, Gilgamesh slays Humbaba for fame and glory.In Akkadian mythology,