His works as a game designer include game supplements for role-playing games , several of which served to establish the basis for products and subsequent development of TSR 's `` Dungeons & Dragons '' game setting Mystara .
His works as a game designer include mostly role-playing games ( RPGs ) . He several of the RPGs served to create the basis for products and following development of TSR 's `` Dungeons & Dragons '' game setting Mystara .