New permanent boss: The Plague

A new Halloween boss that will remain in the game after the event. It will have a unique drop table after the event.
The Plague lair can be entered by talking to 'Halloween' in Edgeville. Afterwards it can be reached by going through the doors at the Ghostly lair underneath the house with bed in high wild, west of the Mage Arena. (The small rooms after entering the doors are safe, while the lair is not).

Inside the lair you’ll need a light source to see any of the monsters around you, this can be done by equipping a lit torch or by lighting a fire. Note: Torches can be bought from any slayer master and need to be lit using Torch Salve (bring plenty of salves!).

The Plague has a chance to extinguish torches and fires, so be prepared to relight either of them regularly.

The Plague will flee to unlit areas during and in between the fight and heal up, so either spread out with torches, light pre-emptive fires, or have at least one person dedicated to chasing the plague with a torch & focusing on melee attacks to keep him from running.

He will fire poisoned bolts, so bring cure poison potions or antidotes.
Ranged attacks now deal full damage to The Plague rather than 1/3rd, but arrows can not be retrieved.
So either bring casts for during melee combat, bring godmage or slayer staff equipment if you want to deal more damage, or bring ranged gear but be prepared to lose the arrows.

During the fight, he will spawn Rats and Zombies to aid in battle, which extinguishes all torches, so be in for a scare when you relight your torch. This happens both randomly and at least once when he reaches half HP. The easiest way to deal with these npcs is to equip a strong melee weapon (dragon sword/axe), so you can kill them off easily without having to equip a torch to land your magic attacks.
Players need to kill their own spawn before they can damage the plague!

In addition! The Plague will deal plague damage to players standing (<4 tiles) nearby. This will heal the plague! Players can use this to their advantage in order to make sure all players deal enough damage for the drop. However, it would be wise to only let one player with a torch stand near the boss to chase it, while others keep their distance, both to not get hit and to not heal the boss unnecessarily.

During the event, The Plague dropped the Plague Mask, Plague Robe Bottom, Plague Robe Top and Lantern. He has since received a new, drop table, which can be found in the Bestiary in-game.
The Lantern drop has been kept as permanent (but extremely rare!) drop on the Plague's drop table.