In the Labyrinth Lord game that I play in (I am Dak, the Steve Buscemi of dwarfs) we had a great encounter with a demigod / powerful devil last session. Exploring a temple hidden deep beneath the manor house of the recently deceased lord of the region, Dak was nearly compelled to worship the altar of an evil god when he touched a magically warded door into the temple fane. Luckily, I rolled a 19 on my save and laughed in the face of evil. And then I got really ticked off, because I have been playing my character as afraid of magic in the first place, and this really struck to the core of my character's fears. I spent a goodly portion of last session destroying the evil altar with my dwarf steel hand ax, even though our good cleric's Detect Evil spell revealed that the evil presence in the altar grew stronger with every blow.
Sure enough, when Dak and Yor (the other party dwarf) succeeded in striking the last blow to the altar in spectacular fashion (collapsing a load bearing pillar onto it), an explosion of green flame occurred and a terrifying four-armed humanoid fish-demon-thing with a long eel-like tail burst into existence over the rubble.
Despite being dwarfs, with our inherently KICK ASS savings throws, we both failed a save vs. paralyzation when the evil fish thing sprayed us with a green liquid which subsequently encased us in a rock-hard goop. The rest of the party looked on in horror from the doorway, with the exception of Innominus the lawful cleric of Indra who warded himself with a spell and dived in to combat. (Thank Indra!)
Dak, terrified as he is of both magic and water, had tied a rope around his waist before entering the partially submerged chamber and tied the other end off on the spikes he had driven in to hold the door open. This enabled my hireling Rodney to pull my paralyzed body out of the fray, but it was obvious that it was going to take several rounds of work by Rodney to chip the coating off and free Dak.
As I was paralyzed and unable to take actions myself, I couldn't help but get involved in the meta-game and I began asking Kom, the player of a character with the ability to make two ranged attacks in a combat round, if he had anything likely to damage the monstrosity. We went through his list of equipment and it turned out that he had little if any magical or dwarf steel missile weaponry (besides his +2 crossbow, which he had already fired and would take a round to reload).
AHA, I thought, when I noticed that he had several vials of holy water written down. Holy water, blessed by a lawfully aligned temple, had to be effective against a chaotic and/or evil being such as this, right?
Kom rolled a solid to hit roll and the vial of holy water splashed across the hideous visage of the slimy bastard... to no avail.
According to Labyrinth Lord, holy water works against undead, period. If this is a faithful emulation of the early game, it seems to me like one of those lacunae in the old rules that occurred through oversight and not intention; after all, the very idea of holy water and its efficacy comes squarely from the catholic church, where it is used precisely to drive away evil spirits and devils. Its not like a lousy 1d8 damage is going to be overpowering any devil anytime soon, but it seems to me like it should do something.
It does make me curious, however, if ANY of the older editions (OD&D, B/X, AD&D 1e) make any provisions for holy water damaging a devil or avatar/agent of an evil god. Being a lazy fuck myself, can anyone find a reference?