King's Bounty: Dark Side focuses on the other side of Teana - the Evil Ones. The player can choose between a fearless Orc warrior Bagyr, a young Demoness named Neoline or a fearsome Vampire named Daert. Each of their worlds have been attacked by the forces of the Light, effectively destroying their homelands and forcing them to flee to the only neutral place and seek refuge among the Dwarves. There, their story intertwines as they meet at the local tavern and bring each other up to speed of the events that have transpired. There they make a blood oath to restore the balance to the world of Teana, and purge the forces of Light from their lands.
Their blood oath didn't sit well with the local innkeeper and they were soon attacked by the guards. While looking for their way out of the dwarven kingdom, they entered the realm of the Dark and upon meeting The Dark One, their quest started to get a shape and their plan was forged. The plan requires an army and a menacing weapon of vengeance to be built. This will require sacrifice and corruption, and depending which protagonist the player has selected, the task will fall to that character. Blackie (which can be renamed), the fearsome dark furry creature is bestowed upon you as your companion which can provide you with tactical advice as well as powerful attacks (upgradeable in the same fashion as in the previous game installments) during combat. Your companion can take a shape of any of the three protagonists and wield powerful attacks upon the enemy.
Aside from new companion (which yields new rage abilities), there are several new unit types, new artifacts, new locations, new trophy achievements, and great many new quests. Many of the quests can be approached in different ways, you can attack certain hero armies head on, or resort to sabotage or subterfuge tactics to weaken the enemy before you strike. While world terrain is reused from the previous installments (lava laden lands of demons, dense forestal paths with points and lakes, snowy mountains), there are many new objects covering these lands that were not present in any of the previous games (shipyard, corn fields, bee hives, etc.) which add a great variety of terrain on each of the maps.