A: First the kills of the player and his pets are merged to a single list. Then for every monster type, the score is calculated with the following formula

Score = sqrt(a) * b * b

where

sqrt(a) = Square root of the number of killed monsters of this type

b = Sum of the attributes of a typical monster of this type

The individual scores of the monster types are then added together. You also get a high bonus for winning, depending on your victory type (the score is multiplied by 2, 3, 4 or 5).