I'd like for guilds to have unique resources that give more character to their classes. I only have so many ideas though..
Reavers (undead melee combat class): "life essence" which is gained by draining fallen player remains. This resource won't generate in any other way.
Harbingers: tarot cards and the "hands" system I mentioned previously.
Vampires: blood as a resource (won't be too significant though) and time of day/room type management.
Druids: trees, forest locations, etc.
Knights of the Swan: ??? Maybe something mask related since swans sort of have masks?
Crow's Crown: ???
Unnamed Corinth mages: ??? Maybe something momentum/fire having things to burn related, so the more consecutive attacks they get off the stronger they become?
Example skill, cauterize: after taking lethal damage, the fire mage doesn't die right away, but will die maybe 10 seconds later if he can't get his flame level up to a certain point to snuff it. Will probably also have a critical hits chance skill, so there should be no "safe" way for allies to let them hit them to get their fire level up. Would have a long cooldown.