Power Bomb
Power Bombs are the ultimate weapon in the Metroid series. They are a heavily upgraded version of standard Bombs, creating a massive explosion of what seems to be nuclear radiation that can destroy Bendezium and defeat many enemies in one blast, including Metroids. They were first introduced in Super Metroid and have appeared in the Prime Series respectively with the exception of Metroid Prime 3: Corruption.
Super Metroid
In their first appearance in Super Metroid, Power Bombs are used to destroy walls and enemies, as well as open Orange Doors.
Metroid Prime
Metroid Prime brought back Power Bombs as a weapon to destroy walls and rubble made of Bendezium. They are a one-hit kill to Metroids. They are found in Phazon Mines.
Metroid Fusion
In Metroid Fusion, Power Bombs retain the same function that they did in Super Metroid, with the addition that they can lure in X Parasites.
Metroid Prime 2: Echoes
Power Bombs remain the same as they did in Prime in Metroid Prime 2: Echoes. They are found after defeating the Power Bomb Guardian under Torvus Bog. In the Multiplayer, a similar powerup called the Death Ball can be aquired.
Metroid Prime 3: Corruption
Power Bombs did not appear in Metroid Prime 3: Corruption at all.