The N'rrgal Colony is the second planetoid of the Twilight Cage visited in Sonic Chronicles: The Dark Brotherhood. After helping the Kron rebel against Nocturnus Clan rule, Sonic and friends set off in search of the remaining six Chaos Emeralds - a journey which takes them to Sector Scylla, and the realm of the N'rrgal.
"Bioelectricity" and "slime" are the keywords to describe this area. The N'rrgal world-fragment is a viridian labyrinth of winding, ooze-filled ravines and luminescant rockfaces. Swarming everywhere are the N'rrgal themselves: translucent green slug-monsters with infuriating regenerative abilities. The moment the Cyclone lands, it is set upon by a swarm of N'rrgal drones who drain the ship's energy, stranding the heroes. Sonic is "politely invited" by the aliens to attend an audience with the hive Queen. As in Mystic Ruins, only Big the Cat is hardy enough to push through the crackling bioelectric fields which weave across the worldlet; with his help, the heroes make it to the Queen's chamber.
The N'rrgal hive mind is disinclined to relinquish her Chaos Emerald, considering it the only deterrant from a superweapon attack by their hated enemy, the Zoah. However, the Queen pledges to hand over the gem if Sonic manages to destroy said Zoah weapon... which sets the heroes en route to their next destination, the Zoah Colony.
The music is a remix of Quartz Quadrant (Good Future and Bad Future) from the US version of Sonic CD.