Haha thanks for playing !
Yes it was challenging to find fun, unique and satisfying upgrade mechanisms, knowing that more unique stuff also means more time to be brainstormed, implemented, tested and balanced. In the end i really love the chaos build and the demonic build, I think they are the funniest to me. The other would have deserved maybe more unique effects that make them fun in their own way, but I'm still very happy with the result :D