Here is a list of things that would have made Chaos a better opponent to fight.
1. Medusa should be able to heal Chaos units just like the Merics.
2. The Marrowkai should be able to send out a demon that possesses enemy units, causing them to turn on their teammates. If such an ability for the Marrowkai was possible, the possessed unit should glow red, so both players would know which one was possessed. The possessed unit would need to gradually lose health over a period of time if such an ability was possible.
3. The crawlers suck, honestly. If they were replaced with hellhounds, so they were bigger, stronger, and could do more damage, that would be awesome.
4. Instead of Eclipsors, there should have been small dragons that could burn enemy units with fire from above, but they would probably need to have health set accordingly so they were not too powerful.
It's unlikely that all, or any, of these ideas could ever be added to Stick Empires and Stick War 2, but they are certainly fun ideas to consider.