Hey folks! Since it might possibly be relevant at tomorrow's game or in future games, I thought I would take this opportunity to explain the system we'll be using to adjudicate combat against spirits at Rage Across the Cape. This system is provisional and not final, and I would love player feedback, but for tomorrow (at least) it's what we'll be using. We've done this and similar things before, but I don't know that it's been written down anywhere, so I'm writing it down here.
The rules given in Laws of the Wild state that spirits use their Willpower for Physical Challenges, and determine damage by their Rage. In practice, this means that no spirit can ever bid more than 10 Traits in a Physical Challenge, which makes the most powerful spirits only slightly better than a vanilla mortal in a fight. This seems to go against the genre of Werewolf in particular, where battles against powerful evil spirits are intended to be trying ordeals and a major part of the struggle against the Wyrm, and not something that a cub with 3 Physical Traits can probably handle on their own by shifting to Crinos.
To that end, spirits in RAtC will resolve Physical, Social, and Mental Challenges by using their Essence to compare on ties. A spirit's "initial" Essence rating is the sum of its Rage, Gnosis, and Willpower. Spirits that are particularly powerful, old, large, tough, etc. receive ad hoc bonus Essence to reflect this power. The Huntsman of the Wild Hunt, a powerful Jaggling, gets 15 bonus Essence according to Laws of the Wild. Incarna avatars and larger spirits may get even more.
As already stated in our House Rules, spirits get one Essence retest on any Challenge. In practice, this means that spirits will tend to come out of the gate very strong, and will become much easier to defeat as they expend their Essence in the fight and take damage.
Challenges that target a Temper will still be resolved by comparing to the spirit's Temper (Rage, Gnosis, or Willpower).