From Sonic Retro
Sector Scylla is one of two (named) regions in the Twilight Cage, visited by Sonic and friends during Chapter 8 of Sonic Chronicles: The Dark Brotherhood. The sector is presumably named after, or lends its name to, Prefect Scylla, an advanced Gizoid who serves as the co-commander of the Nocturnus Clan army.
The N'rrgal and the Zoah keep Sector Scylla in the throes of near-constant warfare, a state of affairs which suits Imperator Ix quite nicely. In the Cyclone spaceship, Sonic visits first the N'rrgal Colony, then the Zoah Colony, managing to collect two Chaos Emeralds (and broker a ceasefire between the aliens to boot).