Nikki and Brie Boulder are the tertiary antagonists of "The Flintstones & WWE: Stone Age SmackDown!"
We first meet Nikki and Brie at the carnival, where they have a kissing booth opened. Fred gets in line but Wilma scolds him for it and makes him leave.
Later, when CM Punkrock and Marble Henry are invited to the wrestling match, they ask the Boulders to join them. At the match, they face Fred and give him a kiss on the cheek for the fans, which Wilma and Betty don't react well to. After CM Punkrock is defeated by Barney, Wilma and Betty chase the twins away.