The Master's Circle is a ring panel obtained in Kingdom Hearts 358/2 Days upon redeeming 358 Mission Crowns at the Moogle. The number of Mission Crowns that must be obtained is an underlined reference to the number of days that Roxas is in Organization XIII.
Effect
It gives 100% protection against elements, but prevents you from healing when you have low health and reduces your health each time you miss with an attack.
While this ring may at first seem more detrimental than beneficial, it may help the player to be better at fighting. The player may learn to aim properly when attacking so as not to waste time hitting air, which may result in losing health to enemy attacks. Missing can also be used to one's advantage, as it allows one to access their limit breaks faster. Strangely enough, Risky Play doesn't affect Xigbar, but the other abilities do.
Besides that, the player can also learn to be on the safe side. Due to the ring's prevention of healing when health is low, players will learn to start healing when a considerable amount of health has been lost. This may let the player pick up the habit of healing early.
