to make lighting or add it to the rain atom

Hmm can you explain this? If you have references I'd like to see those too.

Maybe it could be possible for rain in the game and then the Player is able to choose whether it can be like thunder with it or not.

You can make rain flames..

As for the lightning.. Coding something like that would be a bitch.

Cool idea, but meh.

Giving them physical properties, such as bouncing off the players & ground, will be the worst of it, but having a "background" of it, but placed above the players shouldn't take a lot. I hope.