Adding extra creatures to the castle.

Based on my experience, I would say that both options are promising. Here, the focus is more on the possibilities regarding models and animation sets available to the modder. Why make a catapult out of a goblin? If you can create a goblin of the next tier or its logical continuation? Or you can completely replace all goblins with a new line of creatures. For example, I replaced the Inferno horses with Cerasti (Hammers of Fate, in the past), and the green dragons with Cyclops. In both cases, rebalancing and integrating them into the overall lore was a piece of cake. The main thing is to adequately recolor the models, and that's where the real challenge lies. So, perhaps the question here is more about: 1) The modder's capabilities regarding models and animations for new creatures/tiers. 2) The goals of the mod itself. Does it aim for balance, gameplay mechanics, tournaments, or other goals? Perhaps even adaptations for a specific custom campaign or even a map!