Duplication Glitch
When you get a powerful weapon (Excalibar, Save the Queen) you can duplicate that unique weapon. Get a person the Two Swords Skill and change that person into a knight. Equip the weapon in the right hand and a weak shield in the left hand. Head to any castle and use ''Best Fit'' on that person. You should get a menu that shows that you are buying that weapon you want to dupe. Choose yes. (Does not work with crossbows or anything like that.)

Invisibility Glitch
When invisible, you can receive Experience and Job Points when Jumping on a dead enemy or ally. The game's coding considers removing the Invisibility status a top priority and completely forgets that the target was dead in the first place.

Maximum Job Points
Go to learn something in an ability list that can scroll down (like White Magic action abilities, how it has scrolling because there's so many abilities to learn), then try and learn a cheap one. When it asks you if you want to learn it, and you're at the "Yes/No" window, hold square and push up or down (depending on where you are). If it goes to something that you can't afford, select "Yes" (don't forget to save before this, 'cause it doesn't always work right). If it tried to learn it and leaves you with '0000' Job Points, exit out to the main character selection, then go back to that character's job list; that job should now have '9999' Job Points.