Sin Beast 4: Belphegor
|66||100,000||[Fire, Water or Lightning]|
Therefore its paramount you use the Freelancer's Examine or a Magnifying Glass to keep track of its weakness. Plus it would help a lot if you fielded a party of primarily magic-users. What you can do is Default until you have 2 BP, then cycle through three spells in one turn.
For example, if Belphegor is weak to water, have each magic-user cast Blizzaja, Thundaja and Firaja. That way, your characters can consistently synchronise their attacks with eachother. Rather than end up with a ugly mess of attacks that occasionally heal the sin beast.
You could even put your magic-casters in the Ghost state (using the Patissier's Ghostly Ganache) to take advantage of the Red Mage's MP Free in a Pinch (Ghosts have 0 HP) and the Wizard's Full Charge (since you never use MP because of the former).
In terms of attacks, Belphegor can use Hammer to hurt one, Diffusion Ray to damage the party or three of the ultimate spells--Firaja, Blizzaja and Thundaja. The later can of course can be trivialised by group-casting Elemental Barrier.
Elemental Barrier is also immensely useful for avoiding Sloth, which make your party weak to all elements and dispels all buffs. For best results, combine it with Prescience to always go first. After a while, the wheelchair-bound demon will use Summon Sphere to call in three Spheres.
These spherical foes can use Body Slam to damage one or the -aja spells. More importantly, they possess the same cyclic weakness as Belphegor. Therefore spells that can be group-cast (such as your own -aja spells) are recommended to damage Belphegor and the Spheres at once.
Sin Beast 5: Satan
However each time you attack Satan, it has a chance of triggering Revenge, which increases its BP by 1. With 1 BP, it will use Battle Blade to attack one character at the start of the turn, followed by Two Blades to batter the party. With 2 BP, it will add Three Blades at the end for increased damage.
If you somehow boost Satan to 3 BP, it will finish with Four Blades for a nigh guaranteed KO. To avoid this scenario, you can simly cast Calm (Holy Magic) to negate all of the damage. Otherwise you could use a combination of Winter Storm to stop BP recovery and Undo HP for healing.
Sin Beast 6: Leviathan
Rather than swapping to physical attacks, consider equipping the Black Mage's Pierce Magic Defence ability instead. That way, you don't have to sacrifice your damage output by fielding, say, two physical attackers and two magical attackers who are useless half the time.
For its attacks, High Altitude Leviathan uses Bite to attack one or Blizzaja to deal heavy water damage to the party. If you want, give your healer the Iceflame Shield to shrug off Blizzaja or group-cast Elemental Barrier to shield your party.
Like previous sin beasts, Leviathan has a namesake move--Envy, which lowers your party's defences and dispels their buffs. Honestly, it's not so bad, but you should still be mindful and remember to boost your defences back up (for example with the Performer's Grandship).
Meanwhile, Magic Resist Leviathan uses The Last Light to damage the party or Consume Life to randomly attack the party, with a chance of causing instantly death. To keep your party off the floor, give everyone a Safety Ring or group-cast Status Barrier.
Near the half HP mark, Leviathan will Brave twice for three attacks, before going immobile for two turns. If you can survive the onslaught, this is a good opportunity to deal massive damage and quickly end the fight before the casualties build up.
Sin Beast 7: Lucifer
When it's not raining damage on your party, Lucifer likes to use Pride to dispel your buffs and maximise its stats. As you can imagine, it's not safe having a powered up Lucifer hanging around, so quickly use the Exorcist's Purgation (with Prescience) to return the favour.
Later, Lucifer may Brave to use Mow Down and Blade of Fury, before going immobile for one turn. Both attacks hit hard, so consider buffing your party's physical defence to mitigate the damage. In particular, the buffs from Fencer stances and Special Moves can't be dispelled by Pride.