Nintendo is suing Pocketpair, the developer of Palworld, the game often described as “Pokémon with guns”.

Nintendo and The Pokémon Company said that the game “infringes multiple patent rights”. “Nintendo will continue to take necessary actions against any infringement of its intellectual property rights including the Nintendo brand itself, to protect the intellectual properties it has worked hard to establish over the years,” it said in a statement announcing the beginning of the lawsuit.

Nintendo did not specify which parts of the game it believes violate its patents. But Palworld has been repeatedly likened to Pokémon, and Nintendo announced that it was investigating the similarities soon after the game’s release in January.

The game sees players control a character who, as in the Pokémon games, must make their way through a large open world and capture creatures and then use their skills. Palworld also has notable differences from Pokémon, however – including the fact that its players can use machine guns to attack each other.

It is just the latest controversy to hit the game. Since it became popular at the start of the year, it has been accused of taking mechanics from other games and accused of using artificial intelligence to generate some parts of the game.

There is no evidence that Pocketpair has actually done so, however. And defenders have noted that Pokémon is not the only monster-gathering game, and that the hobby takes its cues from Japan’s popular insect-collecting hobby.

All of the controversies have not been enough to limit Palworld’s appeal. It grew rapidly, gaining 25 million players within its first month.

In a statement, Pocketpair repeated its claims that it had ensured that the game did not violate patents. And it suggested that the legal proceedings could mean that the game develops more slowly.

“It is truly unfortunate that we will be forced to allocate significant time to matters unrelated to game development due to this lawsuit. However, we will do our utmost for our fans, and to ensure that indie game developers are not hindered or discouraged from pursuing their creative ideas.”

It also said that it is “unaware of the specific patents we are accused of infringing upon” and that Nintendo had not given it any specific details.