Eorzea Database

Dual Tank Method - This simply requires two tanks to tank the Hydra straight on avoiding breath damage. Since the ability Trivarium can not be avoided this allows the overall damage of the ability to be mitigated more so than it normally would. Damage dealing classes will DPS as usual and healing classes will heal as usual.

A wyvern will eventually join the battle, when it does all damage dealing classes will need to focus and kill it immediately. The wyvern will cast "Bravery" on the Hydra granting it increased damage. Once the wyvern is dead move back to Hydra.

Several times during the battle the Hydra will move to the center of the arena and use an ability called Fear Itself which is a massive AoE from all three heads, to avoid this everyone (even the tanks) should immediately gather right behind Hydra to avoid the attack.

http://uk.ign.com/wikis/final-fantasy-xiv/A_Relic_Reborn more info here thanks to IGN will add the rest when limit listed.

Journey to Halatali and slay the Hydra.
Defeat the Hydra while using the unfinished relic.

Hydra Abilities
Trivarium: Frontal cone AoE attack.
White Breath: Frontal cone AoE attack.
Radiant Breath: Wide cone AoE attack.
Ball of Ice: Targeted AoE attack.
Ball of Fire: Targeted AoE attack.
Mean Thrash: Rear cone AoE attack.
Fear Itself: Massive AoE attack.

Setup & Strategy
Single Tank Method - This strategy requires a single Paladin or Warrior to move the Hydra as close to an outside wall as possible and run circles around him. This causes the Hydra to spin in circles and makes it easy for a single tank to avoid "Trivarium". Damage dealing classes will DPS as usual and healing classes will heal as usual.

Obtained the item "Interview with a Padjal"
Present this item to Gerolt to continue the quest.
"After a cursory examination of the text, Gerolt declares that he will require some time to make sense of its contents. In the meantime, you are to familiarize yourself with the restored weapon in its current state. Arm yourself with the unfinished (Relic Weapon), make you way to (Beastmen Stronghold) and slay eight (Specific Class Enemy), Eight (Specific Class Enemy), and eight (Specific Class Enemy)."

Dragoon: Natalan - (8) Bloodwings, (8) Fogcallers, and (8) Swiftbeaks

"You have defeated the specified (Beastmen Race). Return to Hyrstmill and report your success to Gerolt."

"You have painstakingly obtained the Alumina Salts. Make your way back to Hyrstmill and deliver it to Gerolt."

"Using the Alumina Salts you brought him, Gerolt adds the finishing touches to your relic weapon. Even as he declares his work over, however, the man believes that there is still something incomplete about it. In order to shed light upon the mystery, Gerolt suggests that you seek out literature surrounding the hero associated with the relic. Perhaps the trader Rowena back at Revenant's Roll will be able to assist you in this endeavor."

"You have consulted Rowena who agrees to procure the literature you seek, for a price. For your part of the deal, you must obtain for her an Amdapor Glyph. Venture into Amdapor Keep in the South Shroud, and procure this artifact."

One often confusing mechanic is Chaotic Chorus. There is no warning upon casting like the Chimera in Cutter's Cry. Players need to pay attention if they have a target indicator flash on their character. This means a large purple orb will be coming their way. The player needs to move away from the party and wait. Once the orb is within a few meters, it will stop moving and explode 2 seconds later. After the orb stops, the player needs to run.

It is imperative to stun and silence the Chimera's Voice abilities at all times. The D'horme Chimera can empower its voices, and this can be determined by the glow of the eyes on its heads. If the dragon's eyes are bright violet, then Dragon's Voice will hit even at melee range, and for increased damage. If the ram's eyes are bright blue, Ram's Voice will wipe the party. If the lion's eyes are red, then Lion's Voice will do massive damage, most likely instantly killing even the main tank. Even without being empowered, these abilities can devastate a party.

In place of a Paladin off tank, you can also use a Bard's blunt arrow to stun both Voice attacks. However, only one person in the group should be stunning or else the stuns will become resisted and the party will wipe.

To finish the party setup for this battle you will want two healers (White Mages and/or Scholars) and fill the final spots with Black Mage, Dragoon, Monk, or Summoner.

Chimera Abilities
Lions Breath: Fire based frontal cone attack.
Dragons Breath: Lightining based attack that sweeps left.
Rams Breath: Ice based attack that sweeps right.
Lions Voice: Fire based frontal AoE attack.
Dragons Voice: Lightning based AoE attack. This has a massive radius, but there is a safe spot within 10 meters of the boss.
Rams Voice: Ice based AoE attack, focused on the boss, with a 10 meter radius.
Rams Keeper: Targeted ice based AoE attack.
Chaotic Chorus: Orb that tracks a random player, then explodes upon proximity.

Setup & Strategy
The fight against the D'horme Chimera can be tricky but with the right setup it's quite easy. Your typical setup should have a Warrior (or Paladin) main tank to control Chimera and a Paladin off tank.

"According to Gerolt, the restoration process involves merging the old with the new - that is, embedding the original relic in a new host weapon. To this end, you must bring him a (Class Specific Weapon) melded with two (Tier III Materia)."

Purchase (or Craft) the class weapon and doublemeld it with specific grade III Materia
Dragoon: Champion's Lance (Materia: Savage Aim III)

You have delivered the materia-enhanced (Class Specific Weapon) to Gerolt. The weaponsmith next directs you to go to the Weeping Saint in the Coerthas Central Highlands, and obtain Alumina Salts form the Dhorme Chimera."

Obtain "Alumina Salt" from a cave in Coerthas
Defeat the D'horme Chimera (Coerthas) while on the job that equips the relic weapon.

Pre-requisite Information

Complete Class Quest
Complete Job Quests
Complete Main Scenario Quest
Complete Aurum Vale (or Dzemael Darkhold)
Access to Amdapor Keep
A Relic Reborn (Starter)

Speaking to Nedrick Ironheart in Vesper Bay
Travel to Revenant's Toll to speak with Rowena.
Travel to Hyrstmill to speak with Gerolt.
A Relic Reborn (Walkthrough)

"Gerolt has reluctantly agreed to lend his expertise to the restoration of a legendary arm of yore. For the first step, the weaponsmith bids you venture within (Enemy Stronghold) in the (Zone Name) to retried the lost (Relic Weapon). Examine treasure coffers to find your prize."
Locate the broken quest weapon from the Beastmen Strongholds.

Dragoon: Natalan

"You have obtained the timeworn (Relic Weapon). Make your way back to Hyrstmill and present the relic to Gerolt."