RTF is a global modification that replaces all towns in the game.

I've started working on the upgrade, but I don't know how to design it yet – with crystals or bats. If the abilities are magical, then the former would be better, but I haven't come up with the abilities yet.

Only by reading and watching your "Creation Chronicle" does one understand how difficult it is to create new units. You are one of those who did not abandon their modding skills and throw them away. This deserves great respect.