Gamma Metroids can be damaged by shooting Missiles at their head and underbelly. They are impervious to attacks from above and the rear, so it’s usually a good idea to stay on the ground rather than jump. Gammas move very fast, too, and they can hit you from a distance with their electricity. A good strategy in rooms with lots of maneuverability is to stay on the ground and fire upward. The Missiles will blast it up or up and diagonally away, so you can just run beneath to fire again. However, make sure Samus doesn’t get stuck behind a wall or under a platform where you can’t hit it, as the electricity will deal Samus lots of damage. Note Gamma Metroids will appear in several tricky locations, each requiring its own strategy.
For Gammas high up in vertical shafts in Ruins Area 3 and 4, a good tactic is to reach a high platform on the right wall and time your shots to hit them from below and in front. Note there is an Energy Ball in the same room as the Gamma in Ruins Area 4 that you can collect if you start to run low.
For the Gamma that appears in the sand pit, first clear some horizontal and vertical space with your beam. This will give you a clearer shot from below.
A similar tactic works in the Sewer System with the room full of webbing. To reach this room, drop down through the Metroid shell and roll through the passage. Immediately clear out some of the webbing with your beam - if you picked up the Spazer or Wave Beam, you can do this rather quickly. Otherwise, you’re likely to waste Missiles on them. Stay on the ground and fire up, but overall be careful - it’s very easy to take lots of damage in this fight.
Also in the Sewer System is another room with an Energy Ball. If you are low on energy, lure the Gamma up high, then drop down and grab the ball.
