I don't think Craig is interested in developing a new section to the battle system (dice rolls) this late in the development stage. As you said, it's up to him though. I may be wrong.
Lets, instead, get to discussing damage, and possible formulation for this Fire Gust idea. I like it, and think it should have the formula
Damage= Attack Level*2+Psy Power
Attack level coefficiant can be raised to 1.5 if thats too high, I don't know how hard a hitter the spriggat is supposed to be, nor what his initial power will be.