Creating a .c2g file using built-in editor?

[H2O]

A c2g File is a script, a text file, use a text editor of your choice to create or edit your own (e.g. vim).
For the basic structure look e.g. at play.c2g from 500.

If you have the cc2 folder as well as the the folder containing the custom c2g script of your set within the games folder, a new c2s and c2h file should be automatically created for the custom set, within its folder, as soon as you play it the first time.
If this is not the case, either you located the new folder not in the games folder, or the c2g script contains errors.