Whilst exploring the Crypts in the Trials of the Luremaster add-on I found an extremely irritating problem with Revenants (when a Crypt Thing teleported a solitary character into an area with several of them); if they are "killed" and rise again before they can be destroyed with fire, they are then IMMUNE to all damage except fire damage! Needless to say this was a most unpleasant situation for my fighter/thief with no fire arrows and on the other side of a locked door from the rest of my party.. Luckily the Fire Kiss dagger eventually saved the day, but I'm almost certain this is a bug (the AD&D Monstrous Manual says that revenants must be destroyed by fire, but makes no reference to them becoming immune to everything but fire..)