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Once you have entered the Phazon Mines, go through many trials and retrieve the plasma beam from the Magmoor Caverns. Once you have retrieved it, go back to the Phazon Mines (through the Tallon Overworld, unless you have power bombs, in which case you can go to the Magmoor Caverns south and blow up the bendezium roadblock and enter that elevator) and go to the Metroid Quarantine B and destroy the metroid in the room and go through the door on the easternmost room. Use the Plasma Beam to destroy the plasma pirate and the frozen power supply. Then, you'll be fighting an omega pirate (the fight will be challenging if you haven't already retrieved the X-Ray Visor). Once the pirate is dead, he'll decompose the phazon to your gravity/varia suit and create your new Phazon Suit.