Setup:
Lightning/Sazh/Hope
You MUST have Lightning as your Party Leader.
Paradigms:
COM/SYN/SYN
COM/COM/RAV
RECOMMENDED:
-Upgrade Axis Blade for Lightning to a max level Enkindler.
-Add accessories that boost ATB Rate% for every character including Lightning. Speed is vital here.
-Having the COM role open for Hope works too, but RAV works just fine.
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1.) Attack an enemy that's capable of killing all 3 characters at once. AoE/Area attacks such as the -ga spells are important here (Adamantoise/Long Gui/High level Marks)
2.) Start in COM/SYN/SYN. Fill up 5 Attack bars, but don't attack the enemy yet. Wait until Sazh and Hope buff everyone with Haste.
3.) Once buffed with Haste, switch to COM/COM/RAV
4.) Attack the enemy until your characters are in Critical HP. (If one character is going to die before the others, [namely Hope] use a potion on them or just equip them with Accessories to even out the damage such as a Gaian Ring if you're fighting an Adamantoise.)
5.) Make sure Lightning is using Attack and not Ruin/Ruinga when the enemy is going to kill her. This will ensure that Lightning is closest to the enemy and will get hit by the area attack. You just have to time it so that all 3 characters would die at the same time.
6.) Right before the enemy attack lands and kills Lightning, use an Elixir and IMMEDIATELY press Start>Retry. (The Elixir doesn't even have to heal, you just have to use it.)
7.) If done successfully, you should have one additional Elixir in your inventory.
8.) Rinse and repeat for as many Elixirs/Items as you want.