Nintendo said Thursday it has filed a lawsuit accusing the developer of a video game jokingly dubbed "Pokemon with guns" of patent infringement.

Nintendo and The Pokemon Company are suing Pocketpair, the Japan-based studio behind the "Palworld" game that became a viral hit when its prototype was released in January.

Palworld — which sold more than 5 million copies in just three days — features weapon-wielding player avatars and monsters that look similar to the creatures of Nintendo's wildly popular "Pokemon" franchise.