Monsters from the Id!!

  I very recently wrote about the impact of certain divinations on campaign worlds. My conclusion was that Detect Evil and Detect Lie were either too limited or too high-level to have a large impact on a campaign but Know Alignment had the potential to change a great deal.
  But it hasn't affected mine. I'll tell you why.

  But, since it is me, I will talk about other things first.

  I find that a great many DMs who play 1e (then or now) fail to properly use the encounter tables. The excellent game blog Hill Cantons touched on this some time ago, pointing out that in inhabited/patrolled areas 25% of all encounters were with patrols.

  Quick aside: I recall being a young man and hearing other DMs lament how the PCs were 'too tough' at 5th-6th level and would often just loot villages, burn down temples, etc. I was always surprised. Once when guest DMing a different group I rolled a patrol encounter - the party (3rd-5th level) was rude and dismissive and actually attacked! As I recall the party was dead or captured in 4 rounds - and upset, accusing me of cheating! Turns out none of them had ever read the rules on encountering patrols and all of them, including the usual DM, thought it was just a bunch of 0-level NPCs. That was an important lesson to me - plenty of people never read the entire rule set.

 
  Another section of the rules on encounters almost never used is - psionic encounters.
  Psionic encounters are mentioned in passing  on the 1e DMG page 174 (which is a page I think very few people have actually read in full) and in detail on page 182. If you haven't read them I encourage you to do so when you have a moment.
  Boiled down, the rules state that if you use psionics in your campaign every time there is a positive check for an encounter the DM must determine if
  A) A psionic power was used in the turn previous to the encounter, or
  B) If a spell that resembles psionics was used in the round before the encounter.
  If either is true there is a 25% chance the encounter will be from the Psionic Encounter chart instead of whatever terrain chart would otherwise be used.
  I have always allowed psionics in my campaigns and have enjoyed them, especially since in almost 40 years of DMing I have only ever seen 5 characters with psionics - they are just so very rare for the good guys and so much fun to use on the good guys. I have had many a DM tell me they don't allow psionics because they are unbalancing for the players to have. I disagree because I think the use of the psionic encounters chart makes psionics not just balanced but maybe for trouble than they are worth.
  The reason I say that is many psionic powers have a duration and are used/useful over time rather than in instantaneous use. A psionic using Detect Magic is probably going to leave it one for a little while. Likewise for a psionic using Body Weaponry in a fight. This means that if you use psionics the chance you will have used them within a turn of an encounter check is, well, fairly high. Let's look at this a bit.

  Assume your psionic individual lives in a village near a city in the heart of the kingdom on the plains (this is all to minimize the odds of an encounter). We will also assume she only uses her psionics during the day (also reducing her odds of an encounter) but that the powers she has [Detection of Good or Evil, ESP, and Precognition] are how she pays the bills as a fortune teller and, therefore, something she uses almost every day. With minimal encounter odds (1 in 20 for location, 1 check during the day for terrain, etc.) this means that she will have 4.5 encounters a year that could be from the psionic chart so, if she is careful, she will probably have 2 psionic encounters a year. We'll be generous and reduce this to one psionic encounter per year. What does that mean?
  Bluntly, she's dead. Oh, sure, the encounter might be with a coatl who merely pauses for a moment on the Astral Plane to say 'huh, a psionic' before he swims along, or it might be yellow mold or tritons or something sure. But it will probably be an encounter with a brain mole, intellect devourer, cerebral parasite, or worse. Sometimes much, much worse. Demon prince worse. So, over the years, the odds of her being dragged screaming into the abyss approach 100%.
  And remember, this is while minimizing the odds!. In the dungeon random encounters are checked every 3 turns! Assuming encounters are 1 in 6 any use of psionics means there is a roughly 33% chance it was within the 10 rounds before the check (and the longer the use the more this chance increases) we can assume that someone using psionics in the dungeon should expect 1 psionic encounter per 9 hours or so of routine psionics use.
  I don't know about you, but to me these numbers make it look like psionics are something saved for emergencies!

  Now, about point B)....
  The spells on the list of those which 'resemble psionic powers' includes:
  All spells that start with Tele-
  All Charms
  All Polymorphs
  All Detects
  And all Cures
  As well as a fair few others, including (but not limited to) all Invisibilities, Heat Metal, Augury, and Feather Fall.

  Wow. Let's look at this a little, OK?
  Jerczy, Ahlissa, Brother Reynaud, and Andor were alert for the invisible assassin as they crept rhough the ossuary. A skilled thief, Andor strained his trained senses to hear the slightest sound. Jerczy's sense were honed from his barbarian upbringing. Br. Reynaud focused his attention on protecting the mage, Ahlissa. Ahlissa had cast Detect Invisibility almost 90 minutes before and continued to sweep for the man sent to prevent their quest from succeeding. 
  Without warning Ahlissa utters a soft cry, clutches her head, and slumps to the ground, sitting in the middle of the cavern. Jerczy and Andor searched for a target as Br. Reynaud checked their companion. She seemed perfectly healthy but her eyes were lifeless and her limbs limp. After a few moments he looked up,
  "We must get her out. I will carry her."
  As the cleric slung her over his shoulders Jerczy hissed to Andor,
  "Do you see anything?"
  "Nothing," replied the halfling, "the only creature in this cave besides us is that wee mole."
  The party hurried back the way they came....

  That's right - those long duration divinations that allow you to look for good, life, charms, invisible creatures, etc. also make it more likely that some horrible monster is going to suck your mind dry!

  I know of at least one DM who disallows psionics in his campaign just because of the psionic encounters chart!

  Personally, I have modified this list of spells so that cures and the clerical versions of detects aren't included and have made some other spells less likely to trigger the final scene from Scanners.
  [please note - the last scene from Scanners is pretty grim and gory]
  But it does point out two important things about some 'core ideas' that went into making AD&D.
  One - the world is dangerous: as I have said before, there are hideous things from beyond the walls of reality waiting to drag you screaming from your beds.
  Two, but a bit more subtle - divinations have consequences: whether the notice of a devil in the astral plane or that your target notices the viewing point of your crystal ball, the fact is that divinations are not telescopes or spy satellites, there is a sort of interaction possible and they are not passive but active and noticeable.