Another thing you should know is how the resistances work in this game. I'm not sure about Longfang's stats, but let's assume he's an ordinary Red Dragon, which has a physical resistance of 50. The resistances work like this: first, if your resistance is R, calculate P = R/(30 + R). In the case of the dragon, P = 50/80 = 62.5%.

This P is the probability to cut the incoming damage in half. So if you use an Implosion which rolls 80 damage, there is 62.5% chance to reduce it to 40. But that's not all: if the damage is reduced, there is ANOTHER roll to reduce the damage, and you get to roll either until you fail, or until you reduce the damage to 1/16 of the original amount. So in the dragon's case, there is 37.5% that it takes the full 80 damage, 23.4% that the damage is reduced once to 40, 14.6% that it is reduced twice to 20, 9.1% that it is reduced thrice to 10 and 15.3% that it is reduced four times to 5.

This weird mechanism has interesting effects. It, for example, explains the following scene that seems to occur quite often: you blast a monster with Incinerate for 150 damage (you had a good roll and the opponent failed to resist). Then you do it immediately again and it's only for 5 damage (your roll sucked and the opponent rolled 4 successes on resistance). That's just how the life goes in this game.

By the way, I don't like Dark Magic too much either. I tried Shrapmetal against some dragons, and one cast wasn't even enough to bring one down. (At dark magic level of ~30.) The math does work out, but that doesn't make the disappointment any smaller.