Ok not to sound like I'm comparing flare to diablo, But I've seen one of the NPC's use a spell that look like that twirly spell in diablo. Is there a way to use this in flare? at present, that fireblast is the best I can do.
Im not sure what skill your referring to but if you saw an enemy use the skill then its probably possible for you to use it too.
If you look in the mods/fantasycore/powers folder, you will see a file called powers.txt, which lists all of the available skills. Each of these powers has an ID. This ID can be entered directly into your save file to give you the skill. You should put the skill into your "actionbar" section of the save file.
Could you be more specifc, which spells you are referring to?
Both where/what you saw in flare and what kind of spell you are referring to in Diablo. (Images would be great :)
Just as Ryan said: flare is very easy to mod and experiment with, so if you already saw it in action within the game, you can get it as well easily.