The barbarian princess - Lewis Trondheim

This series, a best-seller in many countries, starts with the apogee of Dungeon, a mighty castle filled with monsters, trolls and goblins kept by a wily bird, the Dungeon Keeper, and the object of desire of many an uncouth and disgusting form of life (and afterlife) and Herbert the Timorous Duck is assigned to defend it! Thank goodness, the Dungeon Keeper has assigned Marvin the Dragon, a blood-thirsty, uh, vegetarian, warrior, to his side. 4 full stories in one omnibus volume at a new larger size! (Combines the 1st 2 volumes originally published).