As the trophy says, Get 69 stars in AR challenges.
Unlike previous Arkham games, the stars you get on DLC challenge maps do count for this trophy. So if you're having trouble getting 3 stars for a challenge, don't get caught up on it. Just make sure you also do the Scarecrow challenges and you'll have up to 9 challenges where you'll only need 2 stars, or up to 3 challenges which you can skip completely.