Dragon Slayer Gaiden: Nemuri no Oukan is a spin-off from Dragon Slayer series, developed by Agenda and published by Epoch for the Game Boy platform. The game was only released in Japan.

Gameplay differs somewhat from the original Dragon Slayer in that there are now outdoors areas, as well as npcs that send you on specific quests. Combat is still real-time, but a new attack button brings the game closer to other action-rpgs like Zelda.