The old Final Fantasy games have their magic system a bit counterintuitive when it comes to weaknesses.

The one that always surprises me is that grass related creatures are not weak to fire. They still are weak to ice attacks, so at least that's normal. The undead are weak to fire, but I'm not sure why. Maybe because you cremate the bodies?! The weirdest of the bunch is definitely stone creatures being weak to lighting spells. Why?! You'd think flying creatures would be weak to lighting, but they're not that often. You also encounter plenty of toad creatures that you'd think would fry nicely at high voltage, but nope, you'll have a better chance with ice spells.

They're fun games, but they make you wish people would stick to Pokémon rules of magical rock, paper, scissors.