The key can be purchased at the item shop in Burrowell by selecting the blank line within the shopkeeper's list of available items. The fact that the shop sells the key is hinted by a townsperson in Burrowell. Unlike the other keys, the Jailers Key can be purchased multiple times and sold at shops like any normal item.
The Jailers Key is required for accessing several key areas late in the game. In particular it is used to access Rogue Fastfinger's cell, the watergate in Slewse, and the travel gate leading to Rendarak in Beran.
|v · e · dDragon Quest II|
5 Sigils • Celestial skein • Echoing Flute • Eye of Rubiss • False idol • Golden Key • Jailers Key • Moonshard • Ra's mirror • Ship • Silver Key • Subtle shuttle • Sunken treasure • Teleportal • Floodgate key • Windbreaker • Yggdrasil leaf