Strange Town posted a video on YouTube showing what looks like black mist entering the hotel's "Campbell Room" from the left side during the early morning hours of Aug. 5.
White mist then clouds the camera lens.
Investigators said about 10 minutes later, a white vortex appeared even more visible and quickly rotated in front of the camera.
Strange Town is a series where paranormal investigators try to capture evidence of spirits in places said to be haunted in the Austin area.
Guests have reported seeing other instances of paranormal activity at the hotel.
As KENS 5 reported, Magnolia owners Jim and Erin Ghedi began restoring the building in 2013 and opened it to the public for ghost tours.
Before that, it had been vacant for about 20 years. It started off as a two-room log cabin when it was built in the 1840s by one of the original Texas Rangers, James Campbell.
The owners said Campbell was massacred by Comanches and is "seen roaming his cabin" from time to time.
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