You can enter the game by completing laps on an agility course until the talent scout calls you. Also, speaking to the Talent Scout with an Agility cape, Max cape or Completionist cape equipped will allow instant access to the game, and a mask can still be obtained for this.
The mask will automatically be kept on death, unless the player is in the Wilderness. If lost or destroyed, the mask can be retrieved for free from the Talent Scout at any agility course.
As of 7 February 2012, the gorilla mask can be added to the Costume Box in the player owned house.