Welcome to the bonus stage! I thought I'd address this little curio as something you might want to try you on your current/next playthrough of Final Fantasy I.
Proof!
While most people end up reaching the Citadel of Trials and changing to the upgraded classes at around Level 30, it's doable as low as Level 10 (for the entire party; Level 11 on anything but the PSP) or even Level 1 (for three members; the fourth will be significantly higher).
But what's the point of changing class at a low level? The answer is this: Under the upgraded classes, your stat gains are generally higher at level up. While a Warrior may level up from 15 to 16 and gain 2 points for Strength, as a Knight they may gain 4.
It's not an absolute certainty as the results are slightly random, but on average your stats will be noticeably higher if you change classes earlier.
There are two paths for an LLCC playthrough, and I'll outline them here:
All Level 10/11:
Guidelines:
- Run from every single possible battle. This excludes storyline bosses and Piscodemons. The Piscodemon battle in Marsh Cave must have only two Piscodemons in order to guarantee the lowest level on completing the Citadel of Trials -- save beforehand to make sure.
- Save frequently in the Cavern of Earth as Piscodemons are a potential (yet somewhat rare) encounter and are impossible to run away from.
- All four characters must be alive at the end of a boss battle, otherwise it'll skew the experience and mess with your final levels.
Mostly Level 1:
Guidelines:
- One of your party will solo the entire game up to the point where you change classes. You can grind as much as you like as long as the other three party members are KO'd before you win your first battle.
- The Red Mage is the only class that has the same stat bonuses before and after the class change event. If you're planning to use a Red Mage, do this challenge. It's easier than the Level 10/11 challenge (other than Astos and his instant death shenanigans) and the other three characters will have 9-10 more levels' worth of improved stat bonuses.
- Start by outfitting your crutch character in Cornelia, then finding any random battle and defending/healing until everyone else is KO'd.
Whichever path you choose, the order of events is this:
- Cornelia → Chaos Shrine; fight Garland.
- Pravoka; fight pirates to get Ship.
Optional: Play 15 Puzzle on the ship to receive Emergency Exit and Cockatrice's Claw.
- Elfheim → Marsh Cave; fight two Piscodemons to get Crown.
- Western Keep; fight Astos for Crystal Eye.
Note: The Cockatrice's Claw from the 15 Puzzle will one-shot Astos if it works. Save beforehand to make sure it does.
- Matoya's Cave; receive Jolt Tonic.
- Elven Castle; receive Mystic Key.
Note: All Mystic Key doors are optional except for the left treasure room of Cornelia Castle; it is however recommended to get the upgraded equipment from the locked doors, especially in a Level 10/11 walkthrough.
- Mount Duergar; give Nitro Powder to Nerrick to access western ocean.
- Melmond → Cavern of Earth; defeat Vampire to get Star Ruby.
- Giant's Cave → Sage's Cave; get Earth Rod.
- Cavern of Earth; defeat Lich.
- Sail to Crescent Lake; receive Canoe.
- Canoe to Cavern of Ice; defeat Evil Eye to receive Levistone.
- Use Levistone to find Airship.
- Fly to Citadel of Trials; obtain Rat's Tail.
Optional: Use the Emergency Exit to avoid fighting the Dragon Zombie/s guarding the exit. Otherwise your minimum level will be 11. (PSP version only)
- Fly to Dragon Caves to receive upgraded job classes.
The only mandatory fights are Garland, the nine pirates, the Piscodemons, Astos, Vampire, Lich, Evil Eye and possibly Dragon Zombie (without an Emergency Exit).
After fighting Evil Eye, your party should each have 2,478 Exp. On the PSP version, this will leave you at Level 10 with 197 Exp required to reach Level 11. On any other version, 2,478 Exp makes you Level 11 with 756 Exp required to reach Level 12.
Once you've got your upgraded classes, you can proceed through the game as normal, only with much better level up bonuses!