Hydra Castle Labyrinth, originally Meikyuujou Hydra, is a freeware Indie platformer developed by E. Hashimoto, a.k.a. Buster. Now the game has been ported to Nintedo Switch by Rinnegatamante.
The game hearkens back to early “Metroidvania” games like Knightmare II: The Maze of Galious and Legacy of the Wizard: the player explores an immense maze-like dungeon, collecting tools and keys that allow them to proceed deeper. Certain areas are cordoned off from the main dungeon area, and each presents a more linear zone with a boss at the end. The player can find new equipment to make themselves stronger as well.