Nylocas Vasilias is the third encounter in the Theatre of Blood, and spawns after killing off the hordes of Nylocas Hagios, Ischyros, and Toxobolos.
A trio of players fight the Nylocas Vasilias.
It changes its combat style throughout the fight by changing its carapace - blue for magic, green for ranged and white for melee, which is also its weakness. Attacking it with the wrong combat style will cause it to reflect the hit back towards the player as well as healing from the hit.
- The word "Nylocas" is very similar to the hungarian word "Nyolcas", which translates to the number "eight" relating to the eight legs of this arachnid-like creature.
- The latter part of the name of the Nylocas Vasilias likely derives from the Greek term "βασιλιάς"(transliterated, "vasiliás"), meaning "king". Thus, the Nylocas Vasilias may also be understood to be a King Nylocas - a name likely intended to lend credence to its lore and offer insight pertaining to its place in the Nylocas hierarchy - deserving of its role as a boss encounter.
- After an update on 21 June 2018 removing the earlier waves of nylocas, the hitpoints of the Nylocas Vasilias was increased from 2000 to 2500, its magic attack bonus from 400 to 600, and its melee, ranged and magic strength bonus from 40 to 60, 60 and 600%, respectively. This also increased its max hit from 58 to 70, as well as being able to hit harder through protection prayers.