This sector is home to a very large creature the researchers called Serris. It is capable of moving and attacking at ultra-high speed. The more senseless and widespread destruction here may be attributable to Serris.
— Adam Malkovich
Serris is a large serpentine creature kept in Sector 4 (AQA). It is capable of moving at a high rate of speed. Serris later became a host to the X, after Samus deactivated the Level 1 doors allowing them to spread across AQA. Adam gives Samus permission to terminate Serris, out of fear that it might invade other sectors.
As Samus approaches the breeding room she was directed to, she finds only a corpse of the creature. Shortly afterward, Samus battles the Core-X mimicked form of Serris.
Samus can defeat Serris by damaging its head with Missiles or the Charge Beam. After it takes damage, Serris begins moving at an extreme rate of speed, preventing Samus from damaging it. Once Samus defeats it, she may absorb its Core-X and gain the Speed Booster.
Throughout the battle, Serris uses the Speed Boosting abilities to traverse the room at incredibly high speeds. Though Samus has used this ability before, it is an ability intrinsic to Serris, much like the Dachora.
- Serpentine bosses are a common theme in the Metroid series, with most games featuring one.
- Aesthetically, due to their multiple eyes, sharp teeth and 'fins', Serris very closely resembles a Magmoor.
- In the later Japanese version, this creature was renamed "Ishtar" (イシュタル), a name also used as part of the name of its battle theme on the Japanese Metroid Prime & Fusion Original Soundtracks.
- "This sector has taken more damage than expected... I knew the X were powerful and destructive, but still... This seems to be purposeful. We certainly can't rule out the possibility that the SA-X has a high degree of intelligence. I find the X fascinating, especially this SA-X. ...But I digress. This sector is home to a very large creature the researchers called Serris. It is capable of moving and attacking at ultra-high speed. The more senseless and widespread destruction here may be attributable to Serris. No doubt the SA-X released it, but I can't be sure why yet. Serris has returned often to the breeding tank here. Its natural behavior must be to go back to it periodically. It's a valuable specimen, but you have been authorized to terminate it. If you don't, it may invade other sectors." —Adam Malkovich (Metroid Fusion)
- "So Serris had been infected by the X, too... Well, as a result, you recovered another ability. At this rate, you may be able to face the SA-X yet..." —Adam Malkovich (Metroid Fusion)