The Guardian Emerald is a special stone that allowed Knuckles to live through countless lifetimes. It was placed by Pochacamac, against Knuckles' judgement, to ensure the survival of the echidnas. When one Guardian dies, their spirit returns to the Guardian Emerald and lives a new life. As one of the Guardian Robots stated, during one of the reincarnations, something went wrong when the Floating Island fell into disrepair, which caused Knuckles to lose his memory. After his last resurrection, Knuckles destroyed the emerald and used a shard to injure Vichama enough to turn him mortal, which would ultimately lead to his defeat.