Narvi's Belt is often a key card in Dwarf decks for it's amazing flexibility. You'll almost always have the sphere match with Dain. It's not restricted, and you could slap it on a super Gimli or Gloin even outside of a classic dwarf swarm deck. One common use for me is in a Leadership/Lore dwarf deck. I put it on Bifur, along with Steward of Gondor. Then Erebor Battle Master and Test of Will can slot right in.