The Skull is a status effect indicated the user has Multi-way combat activated in the wilderness. The Skull will disappear after the player has left the Wilderness.
Skulled players can only engage other skulled players in combat, and non-skulled players can only engage other non-skulled players.
The Red skull is a status effect which players will gain after winning a round of the TzHaar Fight Pits. The red skull does not appear outside the Fight Pits, and disappears if the player with it leaves the Fight Pits or switches worlds. It will also disappear if another player wins the next round of the Fight Pits. Players with a red skull will not lose their items if they die, as the Fight Pits is a "safe" minigame. The only way to have the red skull outside the fight pits is with a glitch.
Before the Evolution of combatEdit
The skull used to be caused by initiating combat with another player or their familiar in the Wilderness, or by entering the Abyss. Upon leaving the location that caused the skull effect a 10 or 20 (only 20 when it comes to attacking another player in the Wilderness) minute timer starts after which the effect will be removed. If a player dies while Skulled they will lose all of the items they are carrying as opposed to keeping the three most valuable.
- In RuneScape Classic, getting marked with a skull was officially known as setting one's alignment to Evil. 
- In RuneScape 2, the skull was said to be the mark of Zamorak during the Abyss miniquest.
- Sir Renitee used to ask for the player to be skulled for switching to the "Skull" family crest.