Almost forgot this.

Star Ocean 2 - There is an ability you can teach your party leader called pickpocket, which does exactly what it says on the tin while wandering towns. In the fourth village you get to in the game. You can pickpocket an old man who has a magic box/treasure chest item. This item will randomly give you three items. Save the game and then open it. for some reason, the game gives you a high chance of getting a Marvel Sword, a overpowered weapon that increases most of your stats by hundred of points because it's a Disc 2 weapon. Claude will now be practically invincible for the rest of the disc. To make matters worse, thanks to SO2's crafting mechanics, you can actually make Claude's best weapon the Eternal Sphere before leaving the first disc if you improve the right skills and luck out a bit with RNG to get the right items. Honestly, SO2's crafting mechanics seriously break the game, but then again, all of the crafting systems in the series do this.

Kingdom Hearts Dream Drop Distance - The Balloon series of spells. I know it sound ridiculous, but if you want to breeze through this game with little effort, just fill up your command queue with Balloon series spells to watch as they wreck most enemy types.

Persona 2 Eternal Punishment - Not absolutely game breaking, but certainly a huge help. In one of the locations in the game, you'll meet a crazy fortuneteller lady. If you talk to her, she tells you your fortune after you give her your birthday. Now... if instead of putting in your birthday you instead write HASTURCOMEFORTH then you get an odd piece of dialogue. Return to Maya's office and you;ll discover a package on her desk giving you the Hastur material card The King in Yellow. Hastur is a Lovecraftian monster of the Tower Arcana that you can create at level 68 and can only be used by Baofu. He is weak to all types of melee damage but will reflect all magical attacks including status magic and almighty. His skill set is a nasty collection of instant death spells and dark magic, and this Persona allows a special conversation with the Biyarky enemy found in the final dungeon and later parts of the Bomb Shelter. These enemies are brutal as they resist or nullify everything and all of their move sets are group hitting non-elemental spells that can wreck even a high level party. When it talks to them, they hand over Seeds of Escape. Golden Nectar, which is an item that drastically reduces encounters and unlike normal spells like Estoma, this one effects powerful enemies as well as weak ones. Pretty awesome Persona you can get for free. The only real catch is that apparently there is no way to find him without consulting a guide as no one has been able to find the hint that explains the method to gain him. I don't believe even official guides told people, so it may have only been discovered through people looking at the code.

Xenosaga Episode 1: The minigames in this title are ridiculous in that they are fun, and pretty easy. Once you gain access to the casino about midway into the game, you can finally access one of the most broken minigames in the series. Unlike almost every other game I've played that has Poker in it, this one seems to be rigged in your favor. It's ridiculously easy to max out your coins from playing it. Doing so will allow you to purchase the Bravesoul, which is easily the most broken accessory in the game. It works similar to the Power Crisis from Xenogears, or Valiant Knife in FFVI. Xenosaga allows you to actually learn this ability permanently, and equip it to your whole party, making your actual on foot team more powerful than anything else in the game. The casino can also be used as a slow but infinite source of money as you can max out basic items and then sell them at shops for a small profit.

Dragon Warrior III (GBC version only) - If you have the original Gamboy Color version of this game, there is a strange glitch kept in there that involves the Pashishi Tracks. There is some specific criteria, but most of it involves on landing on a square that forces a battle. When you win said battle, you get a strange piece of dialogue that says a great power has come over your hero, and then they will proceed to max out their level. If you're playing a female hero with the Sexy personality, you'll have an absolutely awesome stat growth across the board. The Pashishi tracks become available really early in the game and it doesn't matter which one you're on.