MercurySteam, also known as Mercury Steam Entertainment, is a video game development studio based in San Sebastián de los Reyes, Spain. Founded by veterans of Rebel Act Studios and Konami, MercurySteam is best known for the Lords of Shadow games in the Castlevania series. In 2015, it was reported that MercurySteam was actively interested in pitching a new Metroid game to Nintendo. The pitch was unsuccessful, and a year after the story broke, MercurySteam vehemently denied they were working on such a game despite evidence to the contrary.
On June 13, 2017, Metroid: Samus Returns was announced as a co-effort between Nintendo and MercurySteam. The game's producer, Yoshio Sakamoto stated that he had heard MercurySteam was interested in developing a remake of Metroid Fusion, and reached out to them. Samus Returns was built with MercurySteam's proprietary engine, the Mercury Engine.