This section will cover rotations mostly. It won't be as long as my White Mage guide, but there are still a few things that you need to know as a Black Mage.

Starting from the initial pull, cast Fire III if there's more than one enemy. After you cast Fire III, and if there is more than one enemy in the pull, then Fire II is your friend, unless the Tank specifically marks a single target and that target needs to be DPSed down first and foremost (e.g. Temple Bees in Qarn). Once you're at a point where another Fire II cast would put you under 500 MP, now's your time to cast Flare. Once you cast Flare, then you can Convert, cast Swiftcast, and the Flare again. Got X-Ethers? Great! Use one, and then you can cast Flare a third time!

At this time, you're going to be out of mana. Transpose, and let your mana regen by one tick from Umbral Ice I. After that, start casting Blizzard III. Once your mana is full again, cast Fire III, rinse, and repeat.

For bosses, you'll want to start the pull with a Swiftcast > Thunder III. After that, cast Fire III (after casting Fire III, popping Raging Strikes here is a good idea, if you want). Keep casting Fire I until you're next Fire I cast will put you below 500 MP.

Cast Blizzard III, and while your MP is regenerating, refresh your Thunder III on the boss. If your MP drops below the required amount of MP to cast Thunder III, use Swiftcast, and wait for your MP to regenerate a little, then cast Thunder III. After your MP is full again, cast Fire III, rinse, and repeat.

At level 50, Blizzard II and Freeze become useless spells. You can do much more damage a lot quicker if you skip using those spells and refresh your Thunder III on a target. For multiple targets, Freeze isn't a bad idea, although you shouldn't cast it more than once.

Scathe is absolutely useless as a DPS spell. It's useful if you're trying to pull something, e.g. a Clockwork Squire in ST. As a Black Mage, however, there's rarely any instances where Scathing is a good idea.

And that's all there really is to the Black Mage. Black Mage is burst DPS, and he has some support spells, but they're mostly situational. Pop Manaward or Manawall if you accidentally pull something from a Tank (this will most likely be after a double Flare).