Spectral Swarm
There is the sound of angry buzzing, almost painfully high-pitched as a cloud of spectral insects swarms around the adventurers, their collective glow almost bright enough to be painful. While the swarms of ghostly insects are usually nothing more than an irritant, these have been stirred into a rage.
Divine Power. A use of Channel Divinity triggers an automatic critical success for the party.
Fly Away. The use of fly or similar magic (except levitate ) triggers a success for that adventurer.
Radiant Vulnerability. Use of any spell that deals radiant damage and has an area of effect triggers an automatic success for that adventurer.
Animal Handling checks can calm the swarm or Survival checks can be made to find the sparsest concentration of insects. An adventurer wearing geistblock gains advantage on checks against the spectral swarm, and their allies gain an expertise die on checks against it.
Critical Failure: The insects viciously swarm the party. Each adventurer takes 13 (2d12) poison damage and 6 (1d12) necrotic damage.
Failure: Every adventurer who fails is bitten by the spectral swarm, taking 6 (1d12) poison damage and suffering a level of strife .
Success: The party successfully navigates the swarms.
Critical Success: The party successfully navigates the swarms, losing no time and easily taking a container full of ghostly specimens (worth 50 gold to the right buyer).