Extreme cold is an obstacle faced in Metroid Fusion. Due to Samus having been injected with Metroid DNA at the beginning of the game, sub-zero temperatures become a threat to her until she recovers the Varia Suit.
This vulnerability is displayed in the Sub-Zero Containment and in Sector 5, as the environment is cold enough to damage Samus constantly. In the Sub-Zero Containment Unit, the cold damages her at a rate of 6 units of energy per second, while in Sector 5, it damages her at a rate of 15 units per second and knocks her backwards every 1.25 seconds. This damage is unaffected by varying difficulty modes in the Japanese version.
In addition to supercooled rooms, the Blue X in Sector 5 and Sector 6 will sense this weakness and pursue Samus, dealing damage to her if they come into contact. If the SA-X spots Samus, its Ice Beam will freeze her and deal 200 units of damage.
Once Samus recovers the Varia Suit, she will no longer take damage in cold environments and can absorb Blue X to restore her energy. The Ice Beam will no longer freeze her as well, though it still deals a large amount of damage. Samus completely overcomes her vulnerability to cold temperatures after absorbing the SA-X at the end of the game, restoring her cellular makeup from prior to her X infection.
- Despite being a very large threat, the only cold environment on the beaten path is the Sub-Zero Containment, as Samus is never required to enter Sector 5 until she gets the Varia Suit. In fact, she is urged to avoid that sector until she has the Suit.
- The knockback effect seen in Sector 5 was likely implemented to disallow Samus from using the Speed Booster to break some Boost Blocks required to be able to access the Security Room in the sector, which would be a Sequence Break.
- Although supercooled rooms do not appear in Metroid: Zero Mission, an unused cold damage effect exists within the game's files.