[Zeromus_X]

It's a pretty infamous bug in the original, WSC, and PS1 versions of FFII, if you targetted an enemy or ally with an attack or spell, then cancelled the action of the next character in line, you would still recieve the proficiency points of the previous action that you cancelled.

For example, Maria targets the enemy with a Fire spell. Then, on Guy's turn, you cancel and go back to Maria's turn. Now Maria uses a normal attack. She'll still receive the proficiency from selecting Fire, even though she never actually used it. It's an easier/tedious way of leveling up skills, although it'll be a long haul trying to level up those spells without it. In the DoS version, skills level up at an acceptable rate, making this bug unnecessary even if it existed in that version.

At any rate you can become nigh invulnerable by maxing out your evasion with Shields and beating up your own characters to raise their HP.