Creating a rolling banner
 

Greerings
How do i go about creating a small automated banner with text saying"buy two and get the third one at 50% percent off".
Would like the banner to be mobile too across the home page screen.
Thanks all
x-cart 3.0.12
Diana
sorry my version is 4.0.12

You could use one of the many JavaScript 'tickers' that can be found on hotscripts.com or dynamicdrive.com. I don't recommend them though, effects like that tend to make a site look really amateur.

Alternatively, you could create a much better effect (fade in fade out for example) using an animated .gif or Flash.

Babarosa Gif Animator would get the job done.