Like other generative-AI tools, Seedance can create videos based on short text prompts.
Many of Seedance’s clips are based on real actors and shows and some have gone viral since the launch of its latest 2.0 version on 12 February.
The BBC has found clips online said to have been generated by Seedance showing Star Wars characters Anakin Skywalker and Rey battling with their lightsabres, and Spider-Man fighting Captain America on the streets of New York.
The company has not disclosed what data it uses to train Seedance.
ByteDance had previously said the product had already paused the ability for users to upload images of real people.
The company also said it respects intellectual property rights and copyright protections, and takes any potential infringement seriously.
Disney last year struck a $1bn (£730m) deal with the maker of ChatGPT and video-generation tool Sora, OpenAI, giving the platforms access to 200 characters from its franchises including Pixar, Marvel and Star Wars.