The Ring of Mabron is an artifact that holds the specter of Mabrón, a murdered poet and prophet. It is carried by Wako, a general of the Rintrah.
Mabrón’s ghost is bound to the ring and can be summoned as a spectral witness to the group’s deeds. In the Epilogue, Wako summons the specter before Graz’zt and the Rintrah to narrate past stories. Mabrón perceives the metafictional truth before being silenced and sucked back into the ring.
The ring was part of Wako’s arc in the Contest (the tournament of 1370 DR), with a summons in Sigil for the mission of the crowns.