The Gnomefather is always giving a wedding for his daughter-- Gnomish weddings lasting at least 10,000 years-- and during the wedding, pure Gnomish custom, he cannot refuse any favor the player asks. This is useful for genociding any one specific monster or Composition Type (save for God) or gaining an otherwise one-of-a-kind item. You can also wish for access to his considerable treasure of 10,000 ducats. (Attempting to steal his treasure is unwise.)
Because the four levels of his estate occupy a special branch, they cannot be accessed through Now You See Me, but only through an entrance on the 35th level of the main dungeon guarded by Fat Charlie the Archangel, who can be bribed with the Mama Mia Pasta Sauce.