Really sick game !
I would be very curious to know more about the tools you used to facilitate prototyping, building a good toolset that fit your needs can be really challenging at times :p
I've been using Unity for over 12 years, half that has been indie dev, so I've accumulated a huge library of resources I like to use in every project. Mostly stuff like particle effect packs (JMo), post processing (PSXEffects), utility scripts (code like key collecting), etc. As time goes on and you develop more you find yourself hoarding a lot of reusable material!