Thanks for playing! I'm glad you enjoyed the game. I appreciate your feedback and it gives me some clear actionable steps on what I can improve in the future.
As far as the visuals, the "shadow" effect is done with a timer that creates a new frozen AnimatedSprite copy of the players and changes it's colour. This "ghost" node then reduces it's transparency over time and finally deletes itself after a couple of seconds. I tried some different approaches like using the particle effect system for this, and while you can create a ghost trail, it doesn't work with AnimatedSprites.
The living/dead animation is the players death animation played forward, then in reverse. I split all my nodes in the world into "corporeal" and "spirit". On world change I notify one group to add transparency and the other to reduce it. I also do a color change. Someone told me it could be improved further with sprite masks, allowing you to have alternate versions of tilesets for the spirit world etc. It seems like a good option to explore.