To unlock the Onion Knight as a job, register someone multiple communication IDs on Mog Net. Send seven messages to another player. Send and receive four messages from Topapa. After reading the fourth one, you will receive a message and unlock a mini-quest. Go to Uoul and talk to Topapa. Go to the cave that is to the north of the other cave. Enter, then defeat the three Bombs to get a piece of crystal to unlock the Onion Knight as a job.
To duplicate an item, go to the item menu outside of battle and move the item you want to duplicate into the first slot. While in battle, choose the item menu, then press Up + A. You should see a flash of the equipment screen before seeing the main menu again. Press B to cancel. The item is now duplicated. Repeat as desired. Note: Having more than 99 of one item will cause your game file to glitch.
To get a free Mini spell for your entire party, after dropping out of the dragon's nest, go to the area with the spring and the gnome. Talk to the gnome, and he'll give you a Mini spell. Continue to talk to him until he gives everyone in your party a Mini spell.
You can't use level 8 spells until you level up classes of Devout (White Magic; superior form of White Mage) and Magus (Black Magic, superio form of Black Mage). Level 8 Black Magic spells include Flare, Death, and Meteor. Level 8 White Magic spells include Tornado, Arise, and Holy.
Eureka's legendary items are mainly used by the following: Knight, Ninja, Devout, and Magus. Knights get two legendary items, Excalibur and Ragnarok, which equal a total of 277 attack. Ninjas get the dark sword Masamune, which has 132 attack by itself. Devouts use the legendary item Elder Staff, which casts Cura. Black Mages and Magus use Omnirod which doesn't cast anything, but when used in melee it inflicts gradual petrification.
To easily gain Gil, go to the Town Of The Ancients and speak to the child two stories up the grass hills behind the stairs. He will give you a prize if you ride around the continent. Leave town and head east. Get a Chocobo and ride around the outside of the continent. Go back and speak to the child again to receive your rewards. Sell them, and repeat as desired.
When you run out of MP, it's possible to use certain items instead of. For example, if your Black Mage wants to use Fire but has no MP, go to the item screen and use the Fire Staff. This only work if your character can equip the item that is being used. Not all items work. A few items guaranteed to work include the Ice Staff, Fire Staff, Light Staff, and Salamd Sword.
First, get your characters to around level 60-65. You must have a Devout, a Summoner, a Black Belt, and a Ninja in your party. Put your mages in the back row and make sure that the devout has every white Magic spell in his/her spell book. Afterward, make sure that your summoner has every summon magic available for use. The Cloud of Darkness attacks four times each round. It swipes its hand at your, uses bad breath, casts the spells haste and protect on itself, and uses lightning. After you deplete a portion of it's health, it starts using Particle Beam frequently. The party should have the best armor and weapons equipped, and you want decent defense and magical defense. Everyone should have their share of either ribbons, aegis shields, or onion armor so the bad breath attack won't affect them. Use Arise when ever needed and, when not needed, use Curaja and Curaga every turn. When you use Arise, have everyone else that is standing use an elixir so they won't die. Intend to use up all of your shuriken and elixirs. I killed The Cloud of darkness in about 8 rounds using this technique, and the following party at Level 66:
Luneth: Black Belt
Go through the dungeon a few times to get enough exp to make the battle even easier. A city to the south called "The Village of the Ancients" contains all three level black magics as well as the white magic teleport. I used three mages : 2 red (Luneth and Ingus) and a black (Arc). I made Refia a Monk. Have your red mages cast healing and ice spells. A monk can retaliate easily with the new claws found in the dungeon. If you keep the black mage casting ice spells as well you'll definetly win in a couple rounds. Another thing you should probably do is move them to the back, especially the black mage and the red mages too, if they have enough high level magic MP.
First, make sure you're at least level 20 and have decent armor. The best place to level up your job is around Ur, where Goblins, weakest enemies in the game, are. Have a Bard with a Dream Harp so no potions or MP are wasted. You can reach job level 99 in 98 battles by guarding against goblins, only receiving 1 point of damage from each attack. During each battle, there is a certain number of times based on the number of actions required to level up a job. For example, a Bard requires 5 actions job level 1 to 14, and 6 actions job level 15 and up. You won't need to heal, but if you do then use the Bard's Sing ability every ten battles to remain at maximum HP.
There are special weapons and armor that only the Onion Knight can equip. They are the Onion Sword, Shield, Gauntlets, Helm, etc. Obtain them by fighting red and green dragons. These can be found towards the top of the Crystal Tower and in the "secret dungeon".
To unlock a new dungeon, send seven mails to another player using Mog Net. Then, send four mails through Mog Net to the NPC "The 4 Old Men", and another four mails to "King Alus". Make sure King Alus is the last one you send the mails to. After reading the fourth one you will unlock the new dungeon. Ride on the Nautulus and go east of the floating continent. Once there you will see a shadow in the water. Go underwater and move into the coral to enter a cave. There is no real dungeon here, but there is a difficult Boss, Iron Giant.
In order to obtain the Ninja class, considered to be the strongest class of them all. You must go to Eureka (a sidequest area found in the first floor of Sylx Tower) and go all the way through it. When seeing the final teleport (the one who usually takes you to an area with stores), turn all the way left and you will see a floating staff. By touching it, you'll fight Scylla, who gives you this class when defeated.
To not wait an hour each time to send mail to citizens, first send mail to a citizen through Mognet. Then, go outside of the town you are in, save the game, and turn off the DS. Turn it back on and go to the DS's system settings. Go to the clock and increase the time by one hour. Note: Don't do this if the time is already on hour 23, as this may cause issues with sending mail, including disabling the send feature on Mognet for citizens for a day or two. Now, load the game and go back into town. You should be able to send mail again. Feel free to repeat this as many times as desired. This is useful for speeding up the process for Mognet events.