It is a little bit confusing at first, but if you check out the “Damage Calculation” post that I linked in one of my earlier posts, then you will see that the damage formula is given by:
So, there is a random parameter θ, which is why we get different results even for the exact same scenarios (RNG alert!). Also, the attack (Att) and defense (Def) includes all buffs and debuffs from troops and specials.
The one thing I was confused about was that I thought Jabberwocky does a single attack of 600% when only one enemy is present. But, that is not the case, instead he actually still hits twice with 300% special but on the same enemy, which @zephyr1 kindly corrected me.
Hope, this makes it a little clear. 