A random idea i just came up with is the light coin! it is similair to dark elixer: a rare resource that costs a lot to get. Instead of hero troops it unlocks hero defences. They have 30 levels to upgrade and are very strong, but after they are destroyed they must be rebuild, and that costs gold. you can also make it inactive so it cant be destroyed nor can it be used. What kind of defence it should be I dunno. If you have any ideas plz leave a message :)
I tried to make the light coin. Heres the result!