Very cool effect Niels, super useful! Especially how you get the particle IDs, something that I encounter a need for pretty often but wasn’t sure how to do.
Some clarity for others trying to follow this. I’m not as savvy with module scripting so this took some troubleshooting for me to replicate correctly (mostly…). Thankfully I knew JUST enough to figure it out 
- There is a Source emitter, and another emitter that is reading from the Source emitter. So, 2 emitters.
- I set both to have the same Spawn Burst Instantaneous numbers, and the same Lifetimes (otherwise you get wonky uneven results)
- The ‘Save Connection ID’ script is in the 2nd emitter, under Particle Spawn.
- In that module, depending on your editor build, there may not be a ‘Random Range Integer’ module. In mine it’s called ‘Calculate Random Range Integer’ (gotta’ love that stealth renaming). It works the same.
- The 2nd module script, Read Connection Position, should be in the Particle Update.
- The Sprite Based Line should be in the Particle Update as well, under the Read Connection Position module.
- In the Read Connection Position module I manually set the MaxLength to 500
- If you can’t find the Output param you need, make sure the module is selected, and look under the Parameters tab, under Module Outputs.
- Pay attention to the colors of the in/out lines in the modules. Some of them require you to manually set them to specific param types (ex. in calculating the strength param based on the distance between 2 points, I had to set my Length output manually to a float (right-click on the pin circle and select float). Make sure your colors match (that neon green is a float, yellow is a vector, red is a bool, etc.)