Quick recap
Two years after the first film, Queen Poppy receives an invitation from Queen Barb of the Hard Rock Trolls to unite the tribes. King Peppy explains there were once six magic strings, one for each style (Techno, Funk, Classical, Country, Rock and Pop), and the tribes split after arguing. Poppy ignores the warnings, takes the Pop string and sets off with Branch and Biggie. Along the way they meet the Classical, Country and Funk Trolls and other tribes, and Poppy insists all Trolls are the same. It turns out Cooper, the Troll with the spots who lived in the village, is the son of the Funk king and queen and Prince D's twin brother. Barb captures Poppy and uses all six strings on her guitar to turn the Trolls into rock zombies. Poppy resists, smashes the guitar, and for a moment the music is gone. The Trolls get their colors back by singing together, Barb accepts Poppy's friendship and Branch finally tells her how he feels.