During Halloween Horror Nights at Universal Orlando, several rides are open with little to no wait time. These include:

• Harry Potter and the Escape from Gringotts
• Hollywood Rip Ride Rockit
• Men in Black: Alien Attack
• Revenge of the Mummy
• The Simpsons Ride
• Transformers: The Ride-3D

According to one source, these rides are open during all HHN events. Another source notes that the rides are open during the entire event. However, its important to keep in mind that ride availability may be subject to change, and its always a good idea to check with Universal Orlando for the most up-to-date information.