The Master Synthesist is mentioned several times throughout the game but it is actually fairly difficult to track him down without the assistance of a walkthrough. In order to access the Synthesis Shop you need to defeat an optional boss which can be found in Memoria which can only be reached on Disc 4.
Travel to the second colored-orb that allows you to Save/
Tent (shown in the screenshot below). Prepare the team by equipping any equipment that absorbs or resists Water-based magical attacks.
Equipping a 
Ribbon accessory works wonderfully here while a 
Protect Ring will also suffice to greatly reduce the amount of damage done.
Make sure to equip each of your party members with the 
Clear Headed, Antibody and Body Temp Abilities (if they have them).
Travel one more screen into the ocean area and search behind the rock on the right side of the screen. There is no field icon that appears in the original PlayStation 1 version of the game, so just keep pressing the 
Button.
In the updated PlayStation 4 version of the game they added in an icon to help you find it. Eventually a “Mysterious Voice” will ask “Who dares disturb my sleep? Leave at once, or you will die.” Choose “Don’t Leave” to initiate the battle.
Level: 92
HP: 55,535
Preparation is the key to this fight. Hades will hit the party with a bombardment of negative status effects that will absolutely destroy you if you are not prepared. Hades’ moves include:
Dispel)Hades is susceptible to the Slow status effect and having the Clear Headed, Antibody and Body Temp abilities will help to greatly reduce the amount of damage done to your party members. Try to Steal all four items from Hades before the battle concludes.
Steal:
Reflect Ring (common)
Running Shoes (uncommon)
Battle Boots (rare)
Robe of Lords (very rare)
Drops:
Wing Edge
Elixir
Hades will offer you access to his Synthesis Shop after the battle and will suggest that his best item that he can create requires two 
Pumice Pieces (which you should already have if you have been following this walkthrough).
Be cautious though as you will require the Pumice Piece in order to defeat the most difficult optional boss. The 
Pumice (which can be Synthesized from two Pumice Pieces) can be used to teach Dagger the most powerful Eidolon, Ark. It’s up to you how you wish to proceed.
Hades can also Synthesize the following:
Robe of Lords
Tin Armor
Protect Ring
Pumice
Garnet
Amethyst
Peridot
Sapphire
Opal
Topaz
Lapis Lazuli
Pumice Piece
Save the Queen
Phoenix Pinion
Ether
Make sure that you purchase the Tin Armor if you obtained the Hammer by completing the Stellazzio side quest in Treno. The Tin Armor is the most powerful armor in the game stat-wise by a significant margin. It does not teach any abilities but the stats on it are fantastic. The other items are entirely optional.
Click on the following link to return to the Memoria walkthrough page.
