Here are some unique underworld-themed clan names for you:
- Shadow Syndicate
- Veil of the Forgotten
- Covenant of the Abyss
- Netherbound Legion
- Spectral Dominion
- The Eclipsed Enclave
- Bane of the Underworld
- Cryptic Collectors
- Harrowing Shadows
- Revenants' Alliance
- Doomslayers of the Depths
- Wraithwalkers Guild
- Realm of the Lost Souls
- Infernal Consortium
- Phantom's Embrace
Feel free to mix and match elements or modify them to create a name that feels just right for your clan!