First World BlackFlame EXP Grinding Location
BlackFlames appear on an island north of Crescent Isle and are one of the most rewarding enemies to fight if you're looking to grind EXP and ABP. If you're just looking to farm ABP then I recommend you do the Jacole Cave location and hunt the SkullEaters.
The BlackFlame enemies aren't very difficult, but they are extremely annoying. Let me elaborate... They don't have many hard hitting attacks nor do they have any cheap attacks that mess with your character's status. What they do have though is one ability which decreases your character's level by HALF for the duration of the battle only. On the GBA, SNES and iOS versions of the game this ability is called Dark Spark. On the Ps1 dub it's called BlakShock cause whomever translated the Ps1 version didn't know Japanese that well.
The reason having your character's level halved is so annoying is because it drastically decreases the damage they put out while also reducing their chance to hit the enemy. If you're like me and you enjoy just spamming X while you grind, paying attention to the TV or something else; these enemies you can't do that as efficiently as you'd hope.
What I would recommend is putting a Ninja in your party or have someone in your party with the !Throw ability equipped. There's items you can buy in the town of Rikks, all the way in the northern most portion of World 1 (also known as Bartz's home town). These items can be used with the !Throw skill and they'll immediately defeat all BlackFlames you're fighting.
Aside from LightningSkill, you can also use Poison, Holy, Earth or Wind Magic against the BlackFlames to defeat them quickly. They're weak to all those types of magic but more resistant/may even absorb the other types. Your reward for defeating the BlackFlames is 870GP, 362 EXP, 3 ABP per battle. Since every single encounter on this island is with 5 BlackFlame enemies the rewards are always the same.
Last but not least the BlackFlame enemies here also occasionally drop Speed Drinks which you can use during battle to give yourself an edge or sell in town to afford more weapons, armor, items or whatever it is you may want to purchase.