If mana recovered slowly enough, and mages could pass it on freely between them, the ephemeral force would become a valuable trading commodity on its own.
“ A certain type of demon cannot not be hit by ranged weapons or attacks. Attacks have to be made up close and personal for the damage to mean something. Ranged attacks are to impersonal.
Possibally a way to make the ranged attacks more meaningful would be to coat the arrow head or what not with the shooters blood. Of course, they'd better be a good shot, otherwise they're wasting arrows and already bleeding to boot.
Spells: wizards might have half or no effect, preist might work due to divine intention.”
“ Little halflings are told that if they don't behave, a demon called Santa Claus from a hell of ice will kidnap them and force them to toil making toys.”
“ Whilst exploring underground the PCs discover tube like tunnels stretching for miles, upon further inspection the strange tunnels seem to connect all major cities in the are, what is their purpose?”