No Disgaea is complete without a Baal fight and Disgaea 6: Defiance of Destiny, includes multiple rounds with the most notable overlord in the franchise. In this version, there are easier versions of Baal, which are needed to unlock bigger and better content. However, given the difficulty of the boss, it sounds like an easier task than it is.
Even though Baal features obtainable numbers, his stats require players to have multiple reincarnations. I’d advise getting at least double the first go and then look into debuffs for later attempts.
The best tactic is to burn him as quickly as possible. To do this, I strongly suggest building a team of eight to 10 characters with set roles. You want eight of the characters to either buff or debuff and then have at least one damage dealer and Melodia for support.
For your damage dealer, I suggest getting their weapon mastery up to the cap. This is best done with the Juice Bar. For unique evilities, I suggest getting Magic Moderation (Witch), Evil Eye (Evil Eye) or Bushido (Samurai). This depends on how you want to try to damage the Baal and where your shortcoming is.
Some good Evilities to have are Zombie Revival on both your damage dealer and Melodia. From there, Strong Personality, Hasty Rush or anything that increases damage is best.
With regards to the remaining units, just pick tactics that make sense for boosting your main fighter, as there are many Evilities that support everyone. If you can’t find, buy or get what you need from a quest, look into leveling unique units or reincarnating in hopes of something good coming up.
Surprisingly, this is a two phase fight. The first is against just Baal and then Baal with a bunch of zombies. The ideal tactic is to bring out your damage dealer and kill Baal in a single turn. Unless you build multiple damage dealers, this needs to be done in one turn, so buffs and boosts are ideal. That said, your damage dealer only needs to deal 50 percent or more damage.
As long as you can do that much, Melodia can cast Passionate Approach on your damage dealer and they can take another turn. This is where Magic Moderation is helpful for extremely costly SP skills.
In the event they die, if you still have units on the field you can swap one for your damage dealer and/or Melodia thanks to Zombie Revival. This is also handy because this skill will return all health and SP.