Aside of that, I restructured my code the last 3 hours - to split functionality into separate classes and still avoid cludging everything in a "global"-script (available via "GLOBAL.").
I prefer to split things apart into multiple files for easier reusage in other projects, to avoid dependencies, ... and so on
Pheew .... I really thought that things are way easier in Godot (or Unity?). It is not enjoyable if you need to lookup soooo much stuff instead of just creating your assets, writing some logic and voila. Man, I hope I will once reach the part in the project where I can add some animations (Hooray "game won", "Ohh noeees I die", ...). Think they are more fun then.
Needed to fiddle around with "previously freed instances" - you need to take care on your own of getting rid of old variables - as there is no way to check for "valid instance" yet.
Assume you have a coin object in multiple "node groups" and set the coin to "queue_free()" (remove as soon as idling) and then you access it via one of the "node_groups" the entry is not null, but leads to an "previously freed instance" error.
I also changed the fire animation to be more "comical" one as I assume not all people like to watch stuff burn.