I was 12 and got the game using a discount voucher from white dwarf...
Since I still paint the same way though, that's not a problem to answer

I was still learning to drybrush which is why you see streaks on it.
It was painted black (using some paint found in a pot in the shed), heavy drybrush brown, then bleached bone, then a very light skull white. The same way as the skeletons I had just painted, following the guide from white dwarf...
In retrospect today I don't like the little round circle on each square from the forming process. Another kid in school put artex all over his to try and hide the polystyrene look.
If I were doing it today I would probably with fine sandpaper try to reduce the circles and raised dots, then seal with watered down PVC, probably several coats. Then paint and drybrush away (my drybrushing has improved). That assumes no transit. If it was going to move around something to both seal and protect the polystyrene from damage would be needed, though it held up to my school bag fairly well!