Sharlach (Second boss in Decomus Dungeon)
This is one of the few boss' that is magical damage based. So those with low Magical defense BEWARE!
Abilities:
(Normal Skills)
Distorted Passion:

It's a very annoying skill coz it reduces the MP, making you need to pot mp since there's no other way to get mp besides resting. And by using a mp pot, you can't use a hp pot making you vulnerable, especially if you don't have a healer to heal you hp.
Twisted Mind and Body:

A Physical skill (red) that isn't that great a damage but because it's a DoT, you need to beware if you hp is low.
Contempt Attention:

This debuff if paired together with the previously mentioned skill can be deadly coz your now looking at -600 hp every 4 seconds. So make sure you have a reliable healer to remove the debuff/ heal you well.
Trust Revelation:

This is quite a powerful skill, as it reduces ALL by 70. All referrers to everything from stats to attack to defense and it last for 1 min, so make sure you get your healer to remove it as it'll slow you down on killing the boss.
Coercion Undergo Sacrifice:

This one as you can see is a stun skill, but this skill has a twist. Every time the boss uses Power of Light, he also summons a priest that starts chanting his "sacrifice" to make you stun.
(Special Skills)
Overshadow:
This is a strong magical damage burst attack that has a push back effect. He usually uses it when he "pulls" you to him. I'll tell you hot to avoid this skill.
Power of Light:

This is a self buff that he uses after 50%. He creates a sanctuary around himself and while he's inside it, he's immune to both physical and magical skills/attacks. Also every time he uses Power of Light, he also spawns a priest together with it.
Strategy:
The main point of this guide is for a party with a healer (if you can solo then don't even bother to read this, your too pro to even follow this guide :P )
[Copied n' Pasted]
Okay for this boss your going to want a lot of free open space. I'll tell you why in a min. Essentially, you want to lure him out to the bridge that you just came on:
Once that's done, just attack him normally and ranged class keep ur distance from his Overshadow skill. It hurts a lot. A Good tip especially for those ranged users, when the boss is about to use Overshadow he usually 'pulls' the characs within range to him so while he's 'pulling' you just move away from him and his 'pull' skill is nulled, it doesn't work always, but if you time it correctly, it'll work almost everytime. Also, healers be light on your feet to spam your debuff's and make sure to spam your Heal over Time (HoT) skills. It'll help buffer the boss' DoT debuffs.
Once you get him to around 50%, he's start to spam Power of Light and those summons i mention. What you want to do now is to run back so that you'll lure him out of that circle. Once done, kill the priests immediately so that they can't use the above mention skill and stun you. (Best way to do it is have a lock in the party that pushes the boss from behind (towards the priest and tanker) and take out the summon priest while they're at it, this was the tanker can just solely focus on the boss only and the rest of the party can function to heal/attack.
Soon Sharlach will be dead for he's no match for your teamwork.
CONGRADULATIONS!! You've now defeated the second boss of Decomus Dungeon
Conclusion:
Healers SPAM HoT's and keep your distance so you can remove debuff and remember about moving when he 'pulls' you. Be sure to move/lure the boss out of his sanctuary (Power of Light) when he uses it, as you'll just be wasting your skills/attacks while he's inside it.