A trick that works against Gleeok is that some of Gleeok is dolphin safe to walk on. The wings and body are both perfectly walkable without damage. As long as you don't touch the neck or head, you can pull a "round robin" on him to avoid taking damage at all. Just walk around in circles while hitting Gleeok with beams.
ZC Playing Tricks and Skills
Ohh, how cruel it would be for someone to place damage combos underneath Gleeok then, eh? *evil laugh*