The Earth Tyrant side quest can be completed any time after the party has returned from the Tomb of King Raithwall and completed the events aboard the Shiva airship. However, this is a fairly tough quest that can be difficult at earlier stages of the game.
A party level of at least 30+ is recommended and the walkthrough section covers the completion of this side quest after the events at the Eruyt Village when you return to the Golmore Jungle.
It is recommended that this side quest not be attempted until at least that time and maybe later, depending on party level and setup.
The side quest begins in Rabanastre. Travel to the Westgate and search for a green Bangaa named Rimzat. The Bangaa will ask for assistance clearing out the sandstorms in the Dalmasca Westersand so that he can continue with his studies in the area. Agree to help him and he will suggest that you speak to a man sitting on the fountain in the plaza.
Travel to the Southern Plaza area and search for a man sitting in the center of the fountain named Cotze. Speak to him from the edge of the fountain and he will suggest that you talk to his friend Northon for more information on how to get through the storm.
Northon is located in the Northern Sprawl of Lowtown. He is located just south down the pathway away from Storehouse 5 (the entrance to the Garamsythe Waterway). He is standing next to a red Bangaa and is shown in the screenshot below.
Northon will mention that you will need a Windvane to get through the sandstorm. He mentioned that his half of the split-up Windvane is buried under one of the Dynast-Cactuses in the Westersand.
You need to reach the Windtrace Dunes area but you must reach it by entering from the south in the Shimmering Horizons.
Search the Dynast-Cactoid on the southern wall to find the Wind Globe Key Item. Return to Rabanastre.
Rimzat, Cotze and Northon can now all be found near the entrance to the Dalmasca Westersand in the Westgate zone. Speak to Rimzat to show him the Wind Globe item and Northon will give you the Windvane Key Item.
This will allow you to access the Wyrm’s Nest area and battle the Earth Tyrant. Be sure to save your game at this point using one of the Save Crystals in Rabanastre.
Travel north to the Corridor of Sand and then east through to the Wyrm’s Nest area to initiate the battle against Earth Tyrant, but make sure that you are prepared before you set out with your party.
Level: 30
HP: 73,982
Steal: 
Hi-Potion, 
Tyrant Hide, Tyrant Bone
This optional boss battle will likely be one of the most difficult that you have faced so far. It requires a great deal of preparation depending on how early you attempt it in the game. There are three main difficulty factors that you will have to prepare for:
HP / Defense
Earth Tyrant does not have an extremely large amount of HP, but once it reaches approximately 50% of its HP, its defense will increase by an extremely large amount which will draw out the second half of the battle for an extensive amount of time.
Poison and Strength of Attacks
In addition to having fairly heavy regular attacks, Earth Tyrant’s regular attacks have a chance of inflicting Poison on your party members.
Screwtail
This devastating attack will hit all of your party members for a heavy amount of damage and can become extremely troublesome as the fight drags on.
In order to successfully complete this side quest, you need to prepare to deal with extensive amounts of damage and you need to be very conservative with healing spells and the use of items.
Make sure that you have a tank set up with very strong armor, a good shield and as many HP boosting Licenses as you can. This character should be using 
Shielded Armor which can be purchased from the Garif Trader in Jahara and the 
Shell Shield if available. Make sure that 
Decoy stays active during the entire fight and check the Party Setup page of the Tips and Tricks section for more information about tanking.
You should also do your best to reduce the amount of MP you have to spend healing your party. Conserve MP so that you can outlast Earth Tyrant. This can be done by equipping your tank with a 
Tourmaline Ring to nullify the Poison status effect, equipping characters with Shielded Armor which automatically casts 
Protect on the wearer and equipping a Shell Shield to automatically keep the Shell status effect up (all to conserve MP).
Larsa will use Hi-Potions generously during the fight, so much so that a good tactic is to cast 
Haste on Larsa if you can afford to expend the MP (or if one of your non-healing party members can cast the spell) to keep him attacking and healing quickly.
Lastly, keep Shell and Protect active on all of your party members as Screwtail will hit everyone and Earth Tyrant will sometimes jump to hitting party members other than your tank when Decoy wears off. Use Quickenings if you need to once you’re getting towards the end of the fight.
Other Tactics
You can also use the 
Nihopalaoa trick to take down Earth Tyrant easier using status effects and, if Earth Tyrant is under the Berserk status effect, it will not use Screwtail making the fight much easier. Check out the Nihopalaoa Accessory page for more information. Cast Blind on it afterwards to ensure very little damage is done to your party members.
Here is a brief video demonstrating how to defeat Earth Tyrant. A video demonstrating the Zodiac Age version is included below:
A video of the battle in the Zodiac Age version is included below:
Unfortunately, Rimzat, Cotze and Northon will not provide you with a reward for defeating the Earth Tyrant but you can return to Montblanc to receive 1,200 gil.
The pathway will also clear behind Earth Tyrant leading through to the Dalmasca Estersand. The Earth Tyrant side quest is now complete. Click on the following link to return to the Golmore Jungle walkthrough section.
