I couldn't finish 'em. Looks like this's gonna get complicated.
Although degrading, Hollander is quite a tough enemy. He will start the fight by releasing a poisonous gas. Hollander will mostly summon six Land Worms to distract Zack and although these should be easy to defeat, though they can cast Gravity. Hollander will also release his deadly attack, Dimension Missile, where he somehow brings out a giant missile from his bag and fires it at Zack to deplete around 75% of Zack's current HP, even with a high Vitality stat and Wall active. Hollander will cast either Barrier or MBarrier during the fight. Hollander normally attacks by swinging his bag.
After dodging Hollander's poison gas, Zack should start with casting Wall and Regen. It is important to keep Zack's HP high and if possible, ensure Zack has Raise status. An attack from behind may potentially inflict 9,999 HP damage.