The Skeleton Key is used to open mystery chests in campaigns and multiplayer dungeons, and spawn the Roaming Summoners in multiplayer dungeons.
Mystery Boxes[]
Found in both solo dungeons and multiplayer dungeons. Contain random but useful items, such as Shadow Crystals and Soul Crystals. These require one key to open.
Roaming Summoner[]
Found only in multiplayer dungeons (starting with Claristun). Requires a certain number of skeleton keys to summon a Soul of Barno, which when engaged becomes a mirror match.
Where to Find[]
Skeleton keys can be given away as daily check-in bonus checkpoints. They can also be found in Silver Treasure Chests and sometimes from Guild Altar and VIP wheel.