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. On top of supercooled rooms, the Ice Beam used by the SA-X if it spots Samus can freeze her and deal 200 units of damage.
Extreme cold poses a direct threat to Samus in the Sub-Zero Containment and in Sector 5, as the environment itself is cold enough to damage Samus constantly. In the Sub-Zero Containment Unit, the cold damages Samus at a rate of 2 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. It is also made apparent in the Blue X in Sector 5 and Sector 6, which will pursue Samus, as they know that they are a very large threat to her. Once Samus recovers the Varia Suit, most of these effects become negligible, except for the Ice Beam, which will still deal massive amounts of damage to Samus. Samus overcomes her vulnerability to cold temperatures after absorbing the SA-X at the end of the game, and restoring her cellular makeup from prior to her X infection.
- Despite being a very large threat to Samus until she gets the Varia Suit, 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.