"The wormhole... That's probably what's to blame. It's like a tunnel, one that connects different dimensions together. Except here's the problem, anyone who gets sucked into a wormhole, is sent to an alternate dimension. I see now that Demigra has timed his magic attack so he can cause confusion and distortion of time and space. My gosh... What a nightmare..."
Wormhole are a magic-based portals created by Demigra to cause time distortions throughout history even after his defeat. They appear in Dragon Ball: Xenoverse during the Legendary Super Saiyan Saga and the first and second halves of the GT Saga.
At some point before his defeat in the Crack of Time at the hands of the Future Warrior (and Goku depending on the ending), Demigra used his magic to create wormholes timed to strike at specific points in history to cause various time distortions. According to the Supreme Kai of Time, these wormholes are capable of functioning on their own without Demigra's direct control allowing him to plague the Time Patrol even after his destruction. Though the danger they pose to history and the universe is great they are capable of being destroyed, as the one responsible for the events of the Legendary Super Saiyan Saga was destroyed by in the explosion of Planet Namek in Age 762 and the three that appeared in the GT era are shown to being destroyed by a few Ki Blasts from the Future Warrior. In Age 789 of the GT Era, one of them was able to swallow up Baby Vegeta in his Golden Great Ape form, showing they are capable of swallowing up something/someone as large as a Great Ape.
Like Demigra and Towa, these Wormholes seem to be capable of influencing and empowering villains through Demigra's Dark Magic and even induce Villainous Mode and are apparently capable of controlling powerful villains like Legendary Super Saiyan Broly, Great Ape Baby, Super 17, Nuova Shenron, Eis Shenron, and Omega Shenron.
In Xenoverse 2, Towa is also shown to be capable of creating weaker wormholes which she uses several times in the main story. The first is during the Cell Games when she uses one to connect Age 767 with the alternate timeline from Dragon Ball Z: The Return of Cooler allowing Meta-Coolers to come through the wormhole and join the Cell Games in the main timeline. After defeating the Meta-Coolers, the Warrior uses this wormhole to travel to New Namek and it is later destroyed with a ki blast by Future Trunks. In Age 737, Towa uses one to save Bardock from being killed by Frieza's Supernova, allowing her and Mira to turn him into the Masked Saiyan. Later Future Trunks and the Future Warrior manage to use this event to track Towa and Mira to Age ???. Unlike Demigra's Wormholes, these wormholes are weaker and Towa only seems to be capable of creating one at a time.
Frieza uses a wormhole in order to have his ship access to Conton City, so he can begin his siege on the city.