Completionist cape

The completionist cape is the most powerful cape in the world of Runescape that can be bought in Varrock Museum for 5,000,000gp, if a member has all skills trained up to 99, a Dungeoneering level of 120, have completed all quests, tasks and mini and hidden quests and unlocked all the music tracks, prayers, and magic spells in Runescape. It has the ability of the Ava's Device to retrieve arrows and Ardougne Cloak 4's ability to teleport the player to the monastery and the farming patch north of Ardougne. The completionist cape also counts as a TzHaar fire cape (for fighting ice strykewyrms)

Similar to the Dungeoneering master cape, this cape leaves a trail of white smoke behind the owner. The cape can then be upgraded after completing a list of requirements including 5000 castle wars games and a full statue of Dahmaroc in the players house. The particles on the cape change to gold when upgraded and the black dragon in the emote will change into a gold one.

Emote
As a true gift for players who have managed to achieve this cape, the cape turns the owner into a full fledged adult Dragon with lava cracks and black wings. The player starts off by spitting a jet of fire into the air. Following that, the player flies up and hovers in the air, constantly burning a 5x5 spot around him, shaking the entire screen while doing so. After the smoke has cleared, the classic "R S" symbol melts forth from the molten rocks. The player then growls around before turning back into human form. If this emote is preformed with a trimmed cape, your dragon form will be equiped with a set of golden dragon armour and your wings will have their webs gold-plated as well.

http://images1.wikia.nocookie.net/runescape/images/7/70/Completionist_cape_animation.gif

Requirements
The Completionist Cape was first mentioned in the Capes of Distinction Developers' Blog. The non-trimmed cape will only be worn by players who have:
 * All skill levels at maximum (120 Dungeoneering and 99 in all other skills.)
 * All quests complete (including hidden ones)
 * Every music track unlocked
 * All tasks complete
 * All magic spells unlocked (Spells from Livid Farm, Mage Training Arena, and the Mage Arena)
 * All prayers unlocked (Prayer from Dungeoneering and Camelot training room)
 * All Varrock museum Kudos
 * All Miniquests

Trimmed
To wear the trimmed Completionist cape you will need the following in addition to the previous:
 * 4,000 Chompy kills.
 * Scabarite research complete.
 * Highest rune shop unlocked from Ali Morrisane.
 * All hot-air balloon travel routes unlocked.
 * Eagle transport routes fully unlocked.
 * All Smoking Kills sub-bosses unlocked.
 * Unlock ability to craft all Slayer items and to deliver killing blows quicker.
 * Master White Knight rank obtained.
 * Flying broomstick unlocked.
 * Found all hidden treasure from Making History.
 * Achieve 1,250+ Conquest rank.
 * Unlocked the full power of the Ivandis flail.
 * Played 5,000 games of Castle Wars.
 * Unlocked maximum access to Mobilising Armies rewards.
 * Defeated all champions.
 * Achieve maximum rank in each Barbarian Assault role.
 * Complete all Court Cases.
 * Complete 25 chimp ice deliveries.
 * Find all barbarian notes in the Ancient Cavern.
 * Unlock all rewards from the Artisans Workshop.
 * Obtain all circus clothing.
 * Complete the Dahmaroc statue in your player-owned house.
 * Unlock the 'scroll of cleansing' ability.

Trivia

 * The cape has been enchanted by Dahmaroc, and only players who mastered all skills are able to touch it without being transformed into an animal and cast away.