Diffusion Missiles were a special type of chargeable Missile made by the Galactic Federation. They augment the Ice Missiles. Their only appearance is in Metroid Fusion. It is the fifteenth item collected in that game.
At first, Adam reacts with feigned surprise that Samus acquired the upgrade, stating that it had not received a report from HQ that the upgrade had been sent and it was likely a procedural error. It later states that the Federation was in fact trying to withhold this weapon from Samus, because they feared she would grow too powerful in her attempts of annihilating the X Parasites. However, they already sent it and she found it, accessing it from Sector 4's Data Room.
Diffusion Missiles have a very large blast radius, but only when charged. When charged and fired, the Diffusion Missile creates a shockwave of ice energy that spans the entire screen, freezing enemies, as well as destroying Missile Blocks. This is only necessary once, but is useful in other situations.
They do not use up any more Missiles than would be normally used, even when charged. Whether charged or not, the Diffusion Missile is more powerful than the standard Ice Missile, dealing 12.5% more damage (from 40 to 45), 50% more damage than a Super Missile, and 350% more damage than a Normal Missile. An enemy that takes three Ice Missiles to kill will generally only take two Diffusion Missiles, even if Samus doesn't charge them. It is readily noticeable that the Diffusion Missile launches are much more explosive and powerful than the standard Ice Missiles, seeming to create a visual difference between the two. Once Samus gets the upgrade, the aspect of her missiles will change and they will resemble Super Metroid's Super Missiles.
This upgrade is similar to the Special Charge Beam Attacks for the Ice Beam in Super Metroid, as both the Ice Beam's attack and the Diffusion Missiles spread a sheet of ice that freeze anything it comes in contact with. It is also similar to the Ice Spreader in Metroid Prime.
"Fire Diffusion Missiles while charged to release a powerful blast that damages enemies within a certain radius. Press and hold the R Button then fire the Missiles when charged up."
- When an uncharged Diffusion Missile hits a wall and Samus grabs a ledge, she is still able to hang on. However, when a charged Diffusion Missile hits a wall, it knocks Samus off the ledge, similar to how the Power Bombs and Super Missiles force Samus to let go.
- In the Debug Menu of Metroid Fusion, the Diffusion Missiles are listed as CLUSTE (short for Cluster), implying that the upgrade may have originally been named Cluster Missiles.
- When equipped exclusively, Diffusion Missiles function the same as usual.
| Missile Launcher | Missile | Super Missile | Ice Missile | Diffusion Missile|
Charge Combo | Seeker Missile | Hyper Missile
Ship Missile | Homing Missile
Relentless Missile | Turbo Missile | Missile Key