Rimalkin

From 3kwiki

Rimalkin is a small dungeon with mostly slashing damage

  Small Rimalkin (13,706,540 - 14,425,558) 
  Large Rimalkin (19,607,633 -20,219,030)
  Very Large Rimalkin 25-26M - only 1 exist at the very bottom

  King of Rimalkins - little under 100M. It has a couple lives/200%
  You need to get hidden reps to get to the room. Drops BOP Ring
  of magical deflection. You can't dup that item etc.