EX Boss Guide

ANYWAYS! Welcome to the EX Boss Guide. You can fight the EX boss by beating the game (Which, per se, is pretty hard) then go back to Hein's Castle and talk to the FSII Rematch Crystal. It's on the last page.
...Oh. My. God.
You get to face:
The Final Boss (Hein+Horntail)
EX Drena, Maru, Kishop, and Reyka
With the same amount of time you got on the final boss.
...Yep. You're facing a grand total of 8 Super Powerful enemies with only 11 minutes on the clock.
..Woohoo. Item recommendations time.
Elixirs. (Screw the freaking Barbarians and Magicians, you need EFFIN ELIXIRS for this.)
A. HEALER. I do NOT KNOW HOW I CAN STRESS THIS MORE. I KNOW, BATCH COMMAND.
If %healer%==%no% GOTO YouWillDie
GET IT?
FISHING ITEMS. TUNA SOUPS. YOU WILL NEED THESE.
Zeru's Aegis Barrier: If you even want to try to survive Drena+Maru+Hein+Reyka without this, go jump in a hole. You'll have a better chance of living.
Serene's/Zeika's Immunize: Kishop and Horntail like to poison you while a handful of the others like to possess you.
PROTIP FROM Coder Zeru: You will want at least ONE GOOD MOBBER for this. I swear to God, you will NEED one, either that, or an HP/MP build party.
On the topic of parties, AT LEAST ONE REBIRTH. PREFERRABLY TWO. HELL, RECOMMENDED THREE.
I beat these guys at level 287 (Do the math.)
Amulet of Hope (Self-explanatory...)

Please note, Hein sometimes OPENS THE BATTLE with Despair: Miserable Fate. Be on guard. EDIT NOTE: From experience, he only does this if he has a "Hei-an Stance" from the previous battle. EDIT: Fixed by Zeru
Now, how to beat this monstrosity? There is no easy way out. I fought these guys with a party full of single-hitters.
OPEN WITH BUFFS TO LURE HEIN INTO USING Heian Stance. Hasteo-Pasto, Walls, Aegis, whatever!
AIM FOR Horntail's Left Head, Horntail's Right Head, and Kishop first. Right Head can dispel, Kishop and Left Head casts Aegis Barrier (Which is a pain in the butt.) NOTE: The Right Head can dispel too!
When they're down (And hopefully you're not tearing your hair out,) Aim for Hein and Drena. Maru, HT Center Head, and Reyka won't give you much trouble. Drena, actually, isn't as much as a pain in the butt as the last time you faced her, so make Hein your top priority after the Heads and Kishop.
After that, hopefully you make it in the 11min time margin. (I won. With 3 minutes left.)
Sardonic quote by Zeru: "The EX Boss will take less than 10 minutes."
Me: Hell yeah. You made sure of that. F3

Here's a list of what these guys can do. *Inhales*
Hein: Hei-an Stance, Despair, Ω Dragon Crusher, Possess
Horntail's Center Head: Dragon Breath (Burns), I think he can cast some random status effects too. I never bothered to look at which head was attacking.
Left Head: Aegis Barrier and Healing and Dispellll~
Right Head: Dispel and some status effects (Possess, poison, yadda yadda)
Maru: Wind Strike n' Storm Strike n' Demolition (Watch out for this.)
Kishop: Aegis Barrier, Party Healing
Drena: Spear Crushers S, M, and Ω.
Reyka: Thunder Shot, Most of the time he just triple-shots.

...What? A TRAINING GUIDE? Who the Sam Holy Hill is crazy enough to-...Okay, granted, I am.
If you even want to attempt this, you better have a party of mobbers. (I had a DUAL BUILD. Yes, 999 STR and 999 DEX Zeru, 999LUK 999 DEX Antlan, so on, so forth.) before I tried training on these guys.
Two turns of all my party's mob skills would wipe out anybody except FREAKING DRENA. She has the highest defense out of all of them. But you won't be getting there for a while. Seriously, my Arrow Rain can hit 20k.

That's it. I think some of these guys can possess, but I'm not sure which. Either or, with Immunize, it's not a problem.

Anyways, good luck. You will freaking need it.
EDIT: What you get for facing this monstrosity: 73,804 EXP
17,134 Mesos. Yes, I refought him with my party just to see. The things I do for you people.