Efficiency

Level 5 of the Dungeon
(0, 0, D:5)
  6 gold pieces
(5, 7, D:5)
  a scroll of vulnerability

Level 6 of the Dungeon
[Shop] Kenwir's Antique Armour Shoppe
  (Shop contents are unknown)
(0, 0, D:6)
  3 boomerangs