You can go to the deep dungeon when you have already fought at St. Murmond Holy Place. When you walk up to Warjilis Tade City, you will trigger a scene at the bar. When you leave, a path will open to an island in the East.
This is where you begin the Deep Dungeon subquest. It consists of 10 dark and violent levels: Nogias, Terminate, Delta, Valkyries, Mlapan, Tiger, Bride, Voyage, Horror and End. Each level will open up after you find the exit, then, kill the rest of the enemies. The monsters area always different even if you do the same level again. Also if you are that kind of person this is a great place to poach. There is a fur shop in Warjilis so there are no random battles.
When you are at the last level in the Deep Dungeon you can learn the summon spell “Zodiac” which is cast by the main person, Elidibs. To learn the spell Elidibs must cast the spell on a summoner and the summoner must survive the blow.
(0,6) Elixir (9,4) Kiyomori (2,2) Blaze Gun (0,9) Glacier Gun
(0,4) Elixir (10,6) Elixir (7,2) Blood Sword (1,8) Save the Queen
(0,2) Elixir (12,5) Elixir (6,7) Yoichi Bow (9,1) Mace of Zeus
(12,8) Elixir (4,2) Faith Rod (dont equip this!or the person will leave your party)
(5,0) Kaiser Plate (5,1) Fairy Harp
(0,0) Elixir (6,11) Elixir (0,11) Iga Knife (2,8) Excalibur
(10,9) Elixir (9,8) Cursed Ring (9,9) Secret Clothes (10,8) Blast Gun
(4,4) Elixir (4,14) Elixir (4,10) Sage Staff (4,12) Koga Knife
(2,10) Elixir (3,8) Ragnarok (6,7) Robe of Lords (8,6) Perseus Bow
(1,3) Elixir (2,0) Maximillian (8,4) Grand Helmet (8,5) Venetian Shield
(6,3) Elixir (6,1) Chirijiraden (8,1) Elixir (8,3) Chaos Blade
To master the Summoner job class you must learn Zodiac from the boss on the last floor. To learn it the person learning it must: 1. be a summoner; 2. get hit by it; 3. survive (you can’t use the doubt faith skill). Start out by hitting the guy with either the knight’s Magic Break or the Dancer’s Dillousion skill to get Serpentarious’s Magic attack power down realy low.
Meanwhile have a good attacker take out the other monsters and weaken the friendly one (so he doesn’t finish off the boss before you learn Zodiac). Cast shell on your summoner. That skill (can’t remember the name) that reduces MP instead of HP when you take damage works well.
Also getting your summoner’s faith very low will help you survive but if your faith is too low he’ll use a different attack on you. So if you have low faith get him to cast it on another guy then move the summoner and the guy that’s about to get creamed next to each other before Zodiac hits. This takes time so keep trying.