There's a minor glitch in this battle if you're using AGWS: if you "kill" Tiamat with Jr. or Shion while they're in an AGWS, the game will give you the "Only Jr. and Shion can defeat their pasts" message like it didn't count, but it clearly does count since Tiamat goes down for good when taking him out with the other character.
There's also another odd glitch in that Tiamat's Gravity Blast does FAR less than 1/4 of an AGWS HP; I'm guessing it's basing the damage on the pilot's HP rather than the AGWS'. Good news for us, I guess.
Things you definitely want equipped if you're going with AGWS against Tiamat:
- 2x beam arms *or* 2x gatling guns
- Guard Recovery
- AP Shield
- Cockpit Guard
For weapons, the AG-02 can't equip beam arms, so it has to go with the gatling guns. For the other two, I prefer the beam arms because Tiamat doesn't seem to guard against them as often (in my experience), but the gatling guns will be a better choice if your characters' EATK stats aren't up to snuff.
Shion is equipped with the White Ring so she and MOMO will go before Jr. While their AGWS all have the same speed, this should result in Jr. being the last to go before Tiamat gets its turn, causing the boss to react to him. Tiamat becomes weak against beam attacks (and I'm pretty sure its EDEF goes down, too), allowing the other two to do about 1500 damage with a W-ACT.
Alternatively: if your AGWS are all equipped with gatling guns, you could do the opposite and equip Jr. with the White Ring so Shion's most likely to go before Tiamat. Tiamat becomes weak against piercing (and I'm quite sure its VIT goes down, too) after reacting to Shion, and a W-ACT with dual gatling guns at this point should also do about 1500 damage. In either case, you'll be knocking down its HP pretty quickly.
I have to say, an AGWS strategy is so much easier than characters on foot for Tiamat, for a number of reasons:
- Ruined Earth is quite lethal for characters on foot, and can easily spell game over if he gets two turns in a row after Shion. On the other hand, AGWS can not only tank Ruined Earth fairly well, but Tiamat will also do Deranged Pulse (which is harmless with those AP Shields equipped) instead of Ruined Earth about half the time or so if there's an AGWS on the field.
- This sort of goes along with the above point, but: you don't have to spend the entire battle walking on eggshells over who goes before Tiamat, worrying about it boosting/counter boosting after a certain character (namely Shion). As is usual for an AGWS team, all you have to to is guard and W-ACT until the enemy's dead.
- You don't have to worry about confusion. Sure, you should have picked up the Blade Soul earlier, but that only covers one person. The extractable skill is level 3, which will likely take a decent bit of grinding to get up to at this point, and the search light battles aren't all that quick/easy to farm when you first get to the Encephalon.
However, if you really don't want to use AGWS for some reason (they made disparaging remarks about your mother or something), the best strategy with characters on foot, in my opinion, would be something along the lines of what I used in my older boss fight series for this game:
Game: Xenosaga Episode I: Der Wille zur Macht
Platform: PS2 (played on the PCSX2 emulator)
Developer: Monolith Soft
GSdx 0.1.16 rev.5442 AVX
"Allow 8-bit textures" OFF (game runs much better with this off)
"Alpha correction (FBA)" unchecked
"Enable HW Hacks" checked
"Skipdraw" set to 1 and "Half-Pixel Offset" checked under HW Hacks
FXAA enabled (via PgUp key)
Recommended speedhacks & MTVU hack on.
Using widescreen patch found here (place in "cheats" folder and make sure "Enable Cheats" is checked under System):
Recorded with Elgato Game Capture HD
Windows 7 SP1 64-bit
GTX 670 FTW
Corsair Vengeance 2x4GB 1600GHz
Gameplay and Editing By: Wolfwood824
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