So.... Like CLFM?
Make a notepad file and save it as lua (write in name 'autorun.lua' and change to 'all files').
Then copy and paste the following in it:
tpt.el.bran.name = 'cgas'
tpt.el.bran.description = 'Cold Gas, for tavninder.'
tpt.el.bran.color = 0x009090
tpt.eltransition.bran.tempLowValue = -99999
tpt.eltransition.bran.tempHighValue = 99999
tpt.eltransition.bran.presHighValue = 900
tpt.el.bran.diffusion = 50
tpt.el.bran.gravity = 0
tpt.el.bran.weight = 0
tpt.el.bran.heat = 0
tpt.el.bran.hardness = 0
tpt.el.bran.properties = 2056
tpt.el.bran.falldown = 0
tpt.el.bran.enabled = 1
tpt.el.bran.menu = 1
tpt.el.bran.menusection = 5
It's a gas which diffuses through the whole screen and is cold when spawned.
It also has no resistance against acid and it's color is some kind of dark cyan.
(Btw, you can also use cracker's modloader as autorun and put the script with another name inside a folder called 'Lua'.)
Just a thing: never use that element in saves, unless you want them to only work with people which uses the same script.