So I have been looking for this gamemode everywhere to switch to my server. But I can't find it. Do I have to pay? Or can I not get it? Please help.
Flood is not unique to devinity, there are other servers. However to my knowledge there isn't a version anywhere for public download that works, so you'll have to make a version yourself if you want to host one.
They coded their own version of flood. Communities can host the same gamemode if they can get a copy of code to run for the server.
There's a vanilla-ish version if you're interested in adding your own assets to the gamemode http://steamcommunity.com/sharedfiles/filedetails/?id=474900236