|Location||Saurok Creation Pit, Throne of Thunder|
- Main article: Primordius
- Black Blood — The Viscous Horror spreads its mutated blood to its current target, inflicting 20,000 Nature damage every 3 sec and causing the afflicted player's attacks to coat the enemy in Black Blood, inflicting 20,000 additional Nature damage to Primordius. This effect lasts 60 sec and stacks.
- Deadly Mutagen — If a Viscous Horror gets close to Primordius, the mixture of mutative energies will cause it to explode, inflicting 999,998 Nature damage to all players.
- Patch 5.2.0 (2013-03-05): Added.