Core Keeper is all about exploring caves and crafting items from the resources found during your journey. Terraria's crafting mechanics are also central to the game, as you journey across its side-scrolling voxel world. With such similar premises, a crossover seemed inevitable. Now, Core Keeper developer Pugstorm and Terraria team Re-Logic are finally teaming up. Core Keeper's event page on Steam has the announcement. "Core Keeper and Terraria are both sandbox games with a focus on exploration and adventure," it reads, "and we\u2019ve been in discussion with Re-Logic for a little while now about ways that we could come together to celebrate both games with our respective communities." Turns out the best way to do that is to simply bring a monster from one game into the other. Starting September 26, Terraria's King Slime will be available as a boss summon in Core Keeper. King Slime isn't necessarily the hardest boss in Terraria, but he will be quite a challenge in Core Keeper nonetheless. Pugstorm promises that winning the fight will reward you with some special loot \u2014 we bet it's something slimy. As for Terraria, it's getting Core Keeper's Caveling as a new pet. Normally a common enemy in Core Keeper, this will be a special domesticated version that you can manifest with the right item. Neither developer has spilled the beans on how to summon their respective new creature, leaving players to figure things out when the time comes. That said, these are permanent additions to the respective games, so there's no rush. Both Core Keeper and Terraria have seen success since launching. Core Keeper is still an early access title, but it's kept its fans happy with big content drops like The Sunken Sea update and limited-time events like The Great Egg Hunt. Terraria, meanwhile, has been a massive hit, selling 35 million copies as of March 2021. Since then, it's become the first game on steam to reach one million user reviews, all while keeping its positive rating.