This was my first completion of the game on the PlayStation origins version. I choose to complete the quest with the game's built in default party configuration, which after leveling up to the higher class via Bahamut becomes a Knight (Fighter), Ninja (Thief), White Wizard (White Mage), and Black Wizard (Black Mage). Of course, I stuck with Normal mode instead of the new easy mode because I was craving the challenge of the original NES title.
I begin this walkthrough at the template of fiends with all of my party members at level 41. During the journey through the many levels of the template of fiends I found that brute force was generally sufficient to deal with the hordes of enemies. With the exception of the latter half of the fiends and Chaos battles I generally overpowered the enemies through attacking. I arrive at the final battle with the characters all at level 43.
On the Tiamat floor, I choose to skip the Masamune because my knight was already doing a sufficient amount of damage with the Excalibur. If a viewer wanted to go after this item you would head southeast on the floor immediately following the Kraken fiend battle after descending the guarded staircase.
Once I arrive at Chaos I basically employ the strategy of buffing up my Knight and have him do most of the damage. I begin the battle by putting up a death spell barrier with my white wizard to accommodate protection for the party members without a ribbon or other anti-death protection. Then it becomes a normal pattern of having the Knight, Ninja, and Black Wizard buffing my character with "haste" and multiple "steel" spells to up his attacking power. The white wizard basically keeps the party healthy with "heal 3" or other healing spells, and the occasional "shield 2" spell when healing is not needed. After casting steel a boat load of times my fighter starts doing some decent damage and I have him attack Chaos each round while the Ninja and Black Wizard continue to increase his strength.
Eventually Chaos will fall when you have depleted the 4000 HP he has on this version. I managed to get him before he cast "heal 4", recovering his HP completely.
From there I let the ending and the credits play through, ending this video.