One example: there's a war-horse called Sleipnir, another one Mesmenir, then Shadonir, Leynir and Victanir. They are from the same family of monsters in Final Fantasy XII, very alike each other, although one is pretty much stronger than the other, and you'll find them in different areas of the game.
I was thinking on making horses, for example, having a family of animals similar to it. And in addition to some factions, when they're being used as units, each of those animals would then gain new abilities as they are serving said faction. Also to try and give more variation and life to the world itself.
I'll take the example of horses again. For now, I'd elaborate five distinct species, although they share similarities:
- - Horse (grasslands, hills, etc)
- Pegasus (mountains, snow, etc)
- Unicorn (forest, magic, etc)
- Helhest (volcanic, dark, etc)
- Kelpie (water, ocean, etc)
- When "Pegasus" is being used by a Heaven town, it's trained and improved to "Haizum", which is a spiritual flying horse. Instead of making Pegasus an alreay 'upgraded' unit, you see.
- When "Horse" is being used by a Royal town, it's trained and improved to "War Horse", stronger unit that would be fit as a Knights mount or to be used in War wagons.
- A "Helhest" turns into a "Nightmare" under the Hell banner. Humans use a "Helhest" to charge against group of enemies, by armoring it, naming it "Charger".
- "Kelpies" are turned into "Hippocampi" by Coral, but cannot be used by Hell due their incompatibility to extreme heat and volcanic terrain.
Due some compatibility, the original species can serve in more than only one way to any faction in particular, enabling hiring one, two or even three different units.
It his approach OK to you?
P.S.: This picture below shows the Wolf Genus in that same game. You have the Wolf, then Hyena, Cerberus, etc.