dark messenger
Dark Messenger is a gravity -based attack, that has a unique way of dealing the damage. The only reason I put this on a separate page is because I think it is worth mentioning.
When I first got Diablos, I wanted to try out Dark Messenger immediately. The animation looked cool and whatnot, but he did so little damage. I stopped using him for a while. And then suddenly in like disc 2, I used him and he did massive damage on a fiend. What the? How did it go from no damage to massive damage?
Well, it is because of DM's unique way of counting the damage. The level of Diablos is the percentage of HP taken away from the enemy. So, when Diablos' is on lvl 9, the monster will be dealt 9% damage of his maximum HP (1000HP, damage dealt will be 90HP - 9%). On lvl 20 it is 20%. So when Diablos is on level 100, he will deal 100% of the enemy's HP as damage- until the maximum of 9,999HP is met. Diablos can not go over that figure.
So when killing Tonberries, just keep on using Diablos. No matter what the level, he will most likely deal maximum damage.