True skill mastery

True skill mastery is an achievement greater than skill mastery, obtainable by reaching level 120 in any skill. The achievement was first released on 12 April 2010 with the Dungeoneering skill. When a player reaches level 99 in Dungeoneering, they may continue to proceed to level 120 and receive a Dungeoneering master cape. This is unique to Dungeoneering; thus it is impossible to exceed level 99 permanently in any other skill.

The master cape looks different from the ordinary level 99 skill cape: the skill symbol is lower than on an ordinary skillcape, with particle smoke emitting from the bottom of the cape. The Dungeoneering master cape also has a unique additional emote showing the player killing various Dungeoneering bosses, using all three sides of the combat triangle.

104,273,167 experience is required to reach level 120. This is about eight times the experience needed to reach level 99. Jagex has confirmed that at this time there are no current plans to increase other skills above level 99.

Release for all Skills
Jagex polled to players about plans to add Master capes to all skills. The poll won with 63% of the votes. On 28 April 2014 the Master cape of Accomplishment was released. These capes are awarded for reaching the experience needed for level 120, which is 104,273,167 XP. Skill levels are not increased accordingly, and the Master capes do not have their own emotes. They can be bought from the existing cape sellers for.

Trivia

 * There was once a glitch which, upon reaching level 115 Dungeoneering, would inform the player that they were level 120 on the hi scores. Jagex eventually fixed this to reflect the players correct level.