Gambit System
The Gambit System allows players to tell characters what to do in battle. Those characters do the tasks given, in the order given and only when they're supposed to, all without touching a button during the battle itself. Some Gambits heal a character whose HP falls to a certain amount, Raise a character that has fallen or attack an enemy with a certain amount of HP. Specific Gambits are used when auto-leveling so that characters don't die and don't kill the re-spawning enemies. That way, the fight continues non-stop. The Gambits used depend on the enemy and its attacks.
Helpful Accessories
Quicken the time it takes to reach Level 99 in the game by using some accessories. The Embroidered Tippet doubles EXP earned during battle. Purchase the accessory from the Stranded Merchant in Old Archades. After reaching the Phon Coast, go to the Mosphoran Highwaste and open the chest on the mountain path. It sometimes contains the Embroidered Tippet. Save the game before opening the chest. If the accessory isn't inside, reload the game and try again. Another useful accessory is the Ribbon, which makes the wearer immune to most status effects. Find it in chests in the Cerobi Steppe, Subterra and Henne Mines.
Jellies
The Jelly enemies spawn in the Henne Mines. Pull a switch, and they drop from the ceiling. Equip each character with Mirror Mail. The armor has Reflect so the Jelly's magick attacks will bounce off the equipment and back at the enemy. Do not fight the Jelly until its physical attacks do zero damage. Use the "Foe: Any -- Syphon" Gambit so that each character steals Magick Points or MP from the enemy so they never run out. Set the "Foe: Any -- Charm" Gambit to confuse the enemy, and "Foe: Any -- Break" Gambit to petrify them. They cannot harm the characters, and the characters are not physically attacking the Jellies. It becomes a never-ending battle.
Negalmuur
Find Negalmuur at the Stilshrine of Miriam. The creature spawns Ghasts every few seconds throughout the battle. There are two ways to auto-level with this creature. The first is to set each character with the "Foe: HP < 3000 -- Attack" Gambit so it only attacks the Ghasts, and the "Ally: Party Leader -- Remedy" Gambit so the leader will not die from Doom. The other members must use Decoy so Doom hits them more than the leader. Set other Gambits to heal, Raise and Esuna, as well as Charge so no character runs out of MP. The problem with this is, the fight is over once all the Remedies are gone. Players must keep an eye on the battle when choosing this option. The second option is to have one of the party members use the Haste Gambit on himself, and Raise on the party leader. If the party leader falls, the other party member will quickly bring him back before a new leader enters the battle.