Blood for the Blood God
The pack adds various blood, gore and dismemberment effects to battles in the game. It also adds synced animations between some large units or characters. These effects can be turned on or off via the graphics options.
Blood for the Blood God II adds some unique animations. Foe example, Malekith and Tyrion on foot have some dueling animations. Large units like dragons fighting Carnosaurs or Giants fighting Hierotitans are also added (Personal favorite is one with a Slann fighting most large units).
It has been speculated by some that this DLC was created (rather than being included as part of the base game) because blood and gore effects in a game attract a higher age restriction from many ratings agencies/boards, and so had to be sold separately to the main game if the main game were to keep its original rating. However, there has been no official statement from Creative Assembly to support this claim.