ARTICLE AD BOX
By Tom Richardson
BBC Newsbeat
The makers of an online multiplayer game dubbed "Pokémon with guns" say it's sold five million copies in three days.
Palworld, from Japanese company Pocketpair, has been an overnight success since it launched on Friday.
But its surprising popularity meant players struggled to log on at times due to server crashes.
The game's also been criticised as a Pokémon rip-off due to the similarity of its creatures.
Palworld is described as a "multiplayer monster-collecting game with open-world survival elements".
Players, known as "pal-tamers" travel around a large map battling human foes and creatures known as "pals" which can be captured and recruited.
The monsters can either fight alongside the player in battles, or be put to work at a base, crafting supplies and items for use in the field.
At its peak, the game reported almost 1.3 million concurrent players via Steam, according to tracker website Steamdb, and the team behind it had to hold an emergency meeting to fix early connection issues.
Despite its huge sales, Palworld has not been a hit with everyone.
Its character design in particular has come in for criticism, with people accusing its developer of copying designs from Pokémon.
Reviewers and fans have also pointed out that Palworld's gameplay borrows heavily from survival games like Rust and Ark: Survival.
However, it's been praised for its graphics and has a "very positive" user rating on digital game store Steam, based on 40,000 reviews.
In a message posted on Monday morning, Palworld's developers said their support team had received 50,000 inquiries and was "aware of serious bugs" in the game.
The game has been launched in "early access" - where the version available to players is not the final product.
Fans get to play the game sooner than they might have, and companies are able to raise money towards polishing the game.
But an unfinished version of the game can mean players experience bugs, crashes and other problems.
Pocketpair said it would "share information about the fixes for these issues as soon as possible".