Hecatrice can be discarded to search Valhalla, Hall of the Fallen from your deck.
Darklord monsters are mostly high-leveled Fairy-types. This makes Valhalla, Hall of the Fallen great for bringing out powerful beaters in a Darklord deck. Use Banishment of the Darklords to search out the monster you want to Special Summon.
I doubt Cloudians would even use it. Nimbusman is the only one that can't already be Summoned with Water Hazard or Summon Cloud anyway, neither of which really see play in Cloudians. I'd consider Summon Cloud a straight better card, too.