Well, I think this is new, at least.

Alright, we have various creatures in the game (or coming soon), like spiders, wolves, horses, etc. In some games I've managed to capture a couple of wolves as units.

So, thinking about horses and a good way to add them, as well as to customize each town, or each race, etc, I came to an idea. How about adding various types of stables/breeding farms. But we aren't done there. First, you build a stable (horses), dog house, spider nest, troll pit, rat nest, beehive, etc. These allow you to breed them, but you still have catch them. In otherwords, the various stable types are empty until you catch a pair of them.

Different things can have different ways to acquire them.

1) Catching them can be another quest to go deal with problem xyz. If you build the proper stable first, you can catch them instead of just killing them. Quests to deal with rats, wolves, dragons, etc. These have to be brought back to town safely to activate the various stable / breeding farm.

2) It could be a resource type of tile that is only present in a few locations on the map (like a metal deposit or beehive). You build the stable/breeding farm on top of the tile to gain access. Think Killer Bees, or your mounts to ride.

3) Things like trolls and spiders that are already in the game, randomly wandering about, could have a random chance to capture them after a fight. These have to be brought back to town safely to activate the various stable / breeding farm.

So we have lots of variation and so on. Different critters to fight with, to ride, or to improve a city (dual purposes). For instance bees, could be a breeding ground for killer bees, or harvested for honey... you have to choose based on the type of structure you build. Horses are mounts. Dragons, giant spiders, giant rats, or other large things can be mounts and fighting units (if you have the prereqs from the different trees, as well as the stable/tile/etc to use them). Trolls, spiders, wolves could be fighting units, and with the correct training, could add to the city's sight radius (like they are on patrol or watch dogs).

Finding ways to give these dual purposes, adds to the tech tree. And further makes each town more unique. One town might be able to breed trolls, who's height also lets them see the surrounding area for better defense / sight radius. While the next never managed to find/capture these, but they have a spider farm that you can't get. Maybe spiders can snare/web nearby enemies as a bonus.