there is no, or VERY LIMITED night activity you can expect from Marang. So far i can tell is that you can go for Candat Sotong (see more in Candat Sotong tip) if you're coming around Aug-Oct. Otherwise, just go to the beach and start counting the stars while listening to the beat of the wave from the sea.... or you can have your 'own activity' on the beach!!!
Just relax and listen to the crickets cricking - OR, you might want to try Candat Sotong or fishing for squid. Ask from your hotel the nearest jetty - they usually have candat sotong organised for tourist at the jetty.