Samus's Arm Cannon is her primary weapon. Throughout the game, you'll acquire several beam upgrades that stack, increasing their power and utility. The Charge Beam allows you to hold down the fire button for a more powerful shot. The Wide Beam fires three shots simultaneously, covering a wider area. The Plasma Beam penetrates enemies and certain blocks. The Diffusion Missile, while not a beam, is fired from the Arm Cannon and explodes on impact, damaging nearby enemies and blocks.
