Thunder

I think he means thunder in the map. To put it in a nutshell:

1) Draw a thunder picture, just...plain, yellow thunder...or look it up on google and download a png of it.
2) Import it into map
3) Use envelopes to animate it.

For further details, use the search function. It is there for a reason.

hi

i think i know what you want and i show you my lightning(thunder):

1} you make an color envolpe and make it like this---|
                                                                               V

2}And make an backgraund quad and add then the color envolpe there.

3}Then click on [anim] to see the results.

4}tada the background is flashing.(thundering xD)
<-click to see the flashing!

/lemon

umm you cant see thunder lol. Dont you guys mean lightning? XD