Rather than just screwing with Todbringer, the Beastmen need to effectively torch Bretonnia and the Empire (plus the Dwarf faction if you’re going for the ultra-long victory). Your quest is much the same on the grand campaign, just on a larger scale. For this 12-ish hour campaign you’re automatically in control of Khazrak’s host, and have the task of setting fire to Boris Todbringer’s back yard and pushing over his bins. A tighter map, in this case 52 regions stretching from the Marienberg coast to Hochland, and an emphasis on a specific bit of Warhammer rivalry. In addition, there’s a mini campaign called ‘An Eye for an Eye’ which follows a similar structure to the more focused expansions added to Rome 2 (Caesar in Gaul, Hannibal at the Gates).
Call of the Beastmen adds Khazrak, Malagor, and a whole rabble of goat and bull headed followers to the main campaign (playable if you own the DLC, an AI nuisance if you don’t).