Complete the game to unlock new options for increased difficulty, which can earn you more money, items, and experience points. Note: Playing an additional playthrough is the only way to get the best weapons and shield/armor in the game. It is recommended that you only select Universe mode if you have complete the Galaxy difficulty setting and are over level 90.
Drake's "Crippling Toxin" will make an enemy immobile for a large amount of turns (about 30 to 50 turns depending on the enemy). This will sometimes cause Drake's next turn to glitch and not give you an option to do anything. If this happens, you must exit out of the game to the Dashboard. To make sure this does not happen, use this trick only when you have one enemy in the encounter. If there is more than one enemy, even if you have defeated one, you are much more likely to glitch. Save often when using this to level up. This also works very well with Bosses, although you will still run the chance of glitching the game. Also, Drake should be able to steal a number of items during this time.
Since Aphelion's save points automatically fill up your party's HP and EN, remain close to them. Go all out with the techniques since they are usually powerful and help build up the combo meter. The higher the combo number is, the more powerful your attacks are. Save the game often because a couple bad turns may end up killing your party and requiring a restart from the last save. It is a good idea to grind an area where it will take five or less encounters to level up. Note: You may want to keep grinding until it takes requires than ten battles to level.
The Crimson Ship is an excellent place to level up, but be prepared for some significant damage. In the first area of the ship, you will encounter one enemy at a time. You can use the "Crippling Toxin" glitch without too much of a chance of freezing the game. You should get a little over 13,000 experience points per battle. The second area of the ship will throw two enemies at a time at you; do not use the glitch here. It is recommended that you remain at the first area since the second area encounters usually results in about 20,000 experience points and takes longer.