According to the search results, there are several rides that are open during Halloween Horror Nights at Universal Orlando. Here is a list of the rides that are open during the event:

• Harry Potter and the Escape from Gringotts
• Hollywood Rip Ride Rockit
• MEN IN BLACK Alien Attack
• Transformers: The Ride 3D
• Revenge of the Mummy
• The Wizarding World of Harry Potter – Diagon Alley (Harry Potter and the Escape from Gringotts)

These rides usually have low wait times during Halloween Horror Nights, as most guests are waiting in line to experience the haunted houses. Its important to note that Halloween Horror Nights is a separately ticketed event, and a regular Universal Orlando theme park ticket will not grant you access to the event.