Instructions
First Dhoulmagus Battle
Build a solid defense as soon as the battle starts. Have your casters -- or anyone with a Rune Staff -- cast "Kabuff" to raise your party's defense stat. This will help keep attacks from Dhoulmagus and his clones from hurting you too much. Cast Accelerattle as well to increase your speed and help your party to attack first.
Keep an eye on your party members' health as you fight. Dhoulmagus and his clones are extremely powerful, and you should heal any party member that drops to 100 HP or lower. If Angelo has the "Multiheal" spell, use it liberally since it will heal your entire party, rather than just one member at a time.
Focus on killing the clones to the left and right -- the Dhoulmagus in the center is the real one -- before attacking the center one. The clones have less HP than the real Dhoulmagus -- around 600 HP each -- and will make the fight much harder until they are taken out of the picture.
Cast "Tingle" on any party member Dhoulmagus puts to sleep as soon as possible. You need your entire party fit and fighting to stand a chance of winning this battle.
Re-cast your "Kabuff" spell if Dhoulmagus uses an attack that causes the party to be "Enveloped in a wave of ice." This attack cancels all stat bonuses you may have given your party previously.
Continue striking Dhoulmagus with your most powerful attacks until he dies. Dhoulmagus has about 1850 HP. Make sure you do not finish this battle with low health, as there will be a second battle with Dhoulmagus immediately following this first fight.
Second Dhoulmagus Battle
Heal your party immediately. Dhoulmagus's second form is much stronger and will cause more damage than his first form.
Have Jessica cast "Magic Barrier" and "Insulatle" as soon as possible. Dhoulmagus' second form uses powerful magical and fire-based attacks, and should be defended to minimize their damage.
Use any rune staffs your party might be carrying to raise their defense. Dhoulmagus' physical attacks are also more powerful in this new form.
Attack Dhoulmagus as soon as your defenses are in place. Jessica should use "Twin Dragon Lash" as often as possible, while the Hero and Yang should concentrate on using "Multithrust" and "Helm Splitter," respectively. If Yang has learned the "Executioner" move by this point, have him use that after using "Helm Splitter" to lower Dhoulmagus' defense. Angelo should concentrate on healing the party.
Re-cast your defense spells if Dhoulmagus uses his "Enveloped in a wave of ice" attack. Once the defenses are in place again, continue pounding away at Dhoulmagus until you finally defeat him. This form has about 2600 HP, so you will be in for a long fight.