Ellie

Ellie is a miniature version of the Chaos Elemental that can be unlocked as a pet from the ribs of chaos, which are obtained as a drop from killing the Chaos Elemental. The chance of receiving the item is 1 in 2500, with a threshold of 500 (explanation of drop mechanics). After the item is used, Ellie can be summoned from the pets tab in the hero interface.

Trivia

 * The way Ellie speaks in riddles and seemingly random nonsense is a reference to the Letters to the Chaos Elemental, where the Chaos Elemental often hinted at future content.
 * Ellie's conversation about Varrock is a reference to the 200th quest, Dimension of Disaster.
 * The name Ellie is a pun on its boss's nickname, "Ele".