Dueling Dragons (later renamed Dragon Challenge) was a one-of-a-kind roller coaster when it opened in 1999. It’s two separate tracks (Fire and Ice) did “battle” with one another and featured several close calls. The lift hill was specially programmed to sync the two trains together to always have a perfect ride.
When Universal Orlando added Harry Potter in 2010 they re-themed the ride to better fit their new land. Then in 2015 they stopped dueling after a rider reported injury after being hit by an object allegedly from the other train.
Universal has announced the ride will close forever Labor Day 2017. It will be replaced by a new Harry Potter attraction.