The Boost Guardian.

The Boost Guardian is a boss in the GameCube video game Metroid Prime 2: Echoes. It can arguably be considered not only one of the hardest guardian bosses in the game, though, to some, as one of the hardest bosses in the game period.

The Warrior Ing will oftentimes go into its Morph Ball mode and start to boost around the extremely tight arena. And will deal massive damage when it attacks Samus. Not only that, though during the whole fight, there are absolutely no light crystals, meaning you're constantly loosing health. She can obtain health, however, through the multiple enemy Inglets that roam the stage, which when killed, will release the health she needs to stay alive.