Important: Other than wanting to challenge yourself and getting a trophy, there is no reason to fight this form of the Dark Samsara.
The Dark Samsara’s final form is quite tough and it’s a good idea to level your characters up to around 60-70 before you try your hand at it. You don’t have to do anything special to fight it, as you simply need to go to the main body without destroying any of the four pillars around the area. Four Support Spritnite that every character that’s participating in the battle should have are Commanding Wave, Lifeforce Logic, Iron Vow and Soul Prayer. This ensures that you get an ATB boost, have extra HP and increased physical/magical defense.
Setsuna is ideal here because of both Cure II, as well as Luminaire, with the latter putting Auto-Revive on your characters whenever it is used in Momentum Mode. You might also want to equip her with All-Seeing Eye to give her some extra evasion, since she doesn’t have as much health as the others. Setsuna’s Inspire plus Endir’s Battlecry will make your characters deal a lot of damage; a Momentum’d Battlecry will make Ndir’s Emission tech take a decent chunk out of the Dark Samsara’s health.
Equip everyone with the Talismans that give four Spritnite slots, since you’re going to want all of those slots and it’s a wise idea to strengthen the weapons they are using with Orichalcum, so they are maxed in stats. Although it isn’t necessary to use the Purikka Cobbler Salad for the extra health, depending on what your health is at, it might be a good idea to do it, unless you want to use another food for something like extra defense or evasion.
What makes this fight a lot more challenging than the normal encounter is that The Dark Samsara gains a massive stat boost, as well as access to a bunch of other moves, some of which are more dangerous than its normal moveset. One such skill is Wing Slice, which you might remember as one of Whitewind’s; this skill will likely kill whoever it hits, no matter their HP. It also takes Primeval Tortoise’s Hide in Shell skill, boosting its physical defense (magic still works).
You will also notice that The Dark Samsara will buff its attacks with elemental auras, as well as its regen healing a lot more (310 each tick). Another move it borrows from another bosses includes Gale Rush from Aurorean Tiger, which is the one that hits 8 times (it does around 120 damage each hit) and it’s possible that it can one-shot almost anyone. It also has Schwarzstrom’s Tidal Wave, which hits all characters for aroun 450-500 damage. As you can see, the Dark Samsara has a lot of tricks up its sleeves, but if you keep your characters alive and outdamage its regen, the fight isn’t too hard.