Thie is Hardcore

[Black Mage FF1]

I hate magic classes in FFI, they're a waste.

Solo thief is fun times. Basically as with most solo games, it's about overleveling. I have a few suggestions for later on. White shirt will be great. Using Invis on yourself can help dramatically, in any solo game without magic. That's my best piece of advice for the later part of the game. Yes it takes an armor slot, but later in the game, you'll be dieing easily even with the thief's best armor. It's a more than worthy sacrifice.

THE JACKAL

Why do that when you can use the defense sword and cast ruse on yourself?

The defense sword and the heal staff are two very important weapons to have in a solo thief game. I wouldn't have been able to beat it without them. So make sure you keep them when you get them. But I'm sure you knew that already.