Anyway, these are the substantial errors I've noted in my own print copy of the Advanced Labyrinth Lord rulebook. I've left out trivial typos (misspellings, misplaced commas, etc.) in favor of things that might actually cause confusion or unintended results during play. I hope you find it useful. This is a work in progress and will be periodically updated.
When compiling this information, my decisions regarding what to include were informed by two assumptions:
1. I assumed that the goal was to make every class, spell, monster, and magic item as close in function to the source material as possible. In some cases, it can be difficult (or impossible) to determine if a deviation from the original material is an error or intentional. Any known intentional deviations (such as plate mail armor being more expensive than it is in B/X D&D) were omitted.
2. Whenever a class, spell, monster, or magic item appears in both B/X D&D and AD&D, I checked it against its B/X version, as Labyrinth Lord is primarily based on that edition.
Includes contributions from: Bearbottle0, ken-do-nim.
Latest update: 11 August 2021.
Page 5, Introduction: "You've taken the first step on your adventure, but you are still a 0 level human." The concept of 0 level humans is addressed obliquely here (as well as on the Attack Value and Saving Throw table), but it is never clearly defined, as it is in the Basic rulebook's "Normal Human" monster entry. The guidelines for determining a 0 level human's hit points, for example, are not present in ALL.
Page 7, Creating a Character: The Attack Value tables are on page 112. Saving Throws are detailed on page 106.
Page 23, Illusionist Spell Progression: The reference to the spells Find Familiar and Write in the footnote should be replaced with Summon Familiar and Scribe, respectively.
Page 24, Monks: Interestingly, this version of the monk is unique within ALL in that it seems to based primarily not on AD&D, but rather on the older Blackmoor supplement. It's generally quite accurate, although there are a few differences, such as Blackmoor specifying that monks gain access to the Speak with Animals ability before the Speak with Plants ability and never become immune to poison. It's possible that these are intentional changes, however. Additionally, monks may not use potions or scrolls, nor may they employ any retainers or other hirelings before reaching 6th level.
Page 25, Paladin Level Progression: AD&D paladins gain +3 hp per level after level 9, the same as fighters. Since fighters in Labyrinth Lord only gain +2 hp per level after 9th, however, paladins probably should as well in order to reflect the original intent.
Page 26, Rangers: The permissible alignments for rangers could be more clearly explained. AD&D rangers are required to be Good or forfeit their special abilities and permanently become regular fighters (similar to paladins). ALL states, "They adhere to their own sort of morals, such that they might be lawful, chaotic, or neutral with their larger world views, which may not reflect their disposition to other beings." This sounds like a complicated way of saying they can be of any alignment, but what does "their own sort of morals" mean?
Page 30, Exchange Value: Per this chart, 1 platinum piece is equal in value to 10 gold pieces, not 5 as in both B/X and AD&D. This change may or may not be intentional, but be aware that it has the potential to drastically increase the value of platinum treasures found in modules created for those older rule sets.
Page 31, Adventuring Gear and Items: The small silver mirror, small steel mirror, large belt pouch, large sack, small sack, saddle bag, and wine should each weigh 1/2 pound. The empty flask is given a weight of 1 1/2 pounds, but this is somehow more than the 1 pound weights given for flasks full of holy water or oil, so 1/2 pound is likely correct.
Page 32, Food, Drink, Provisions, and Lodging: Bottles of mead, common wine, and good wine should each weigh 1 1/2 pounds.
Page 33, Animals of burden: Despite the carrying capacities here being indicated for "most horses and mules," all horse varieties listed in the monster chapter (page 162) can carry significantly more.
Page 38, Control Weather: The area of effect is 4d4 square miles.
Page 39, Cure Disease: "The victims of this disease cannot be cured of damage from other spells...." The word "from" in the above sentence should be replaced with "by" to convey the correct meaning.
Page 41, Glyph of Warding: The duration is permanent until triggered.
Page 42, Lower Water: The correct area of effect is ten square feet per caster level.
Page 42, Part Water: The range should be 20' per caster level.
Page 44, Resist Fire: The saving throw bonus should be +2, not +3.
Page 47, Commune with Nature: Range is 1/2 mile per level.
Page 53, Snare: Duration is permanent until triggered.
Page 55, Tree Stride: "However, if the nearest oak tree in range is to the west, the caster emerges from that tree instead." The word "nearest" above should be replaced by "only" to preserve the original meaning.
Page 57, Implant Emotion: Duration should be defined as the length of time the caster concentrates on maintaining the spell.
Page 58, Invisibility, Greater: This is a 4th level spell.
Page 58, Major Creation: It should be noted that the caster may create mineral objects with a duration of 6 turns in addition to vegetable objects of 12 turns duration via this spell.
Page 59, Prismatic Wall: The maximum dimensions of the wall are 4' wide and 2' tall per caster level.
Page 62, Antipathy/Sympathy: The maximum area that can be affected is 10 cubic feet per caster level. If cast on an object instead of an area, victims suffer a -2 penalty to their saving throw rolls.
Page 64, Comprehend Languages: The range and duration for this spell are swapped and should be transposed.
Page 64, Cone of Cold: Victims are entitled to a saving throw. Success results in 1/2 damage.
Page 66, Dimension Door: Unwilling targets should receive a saving throw.
Page 68, Explosive Runes: Duration is permanent until triggered.
Page 68, False Trap: The AD&D version of this spell (Leomund's Trap) has a duration of permanent. It is unclear if the ALL duration of 6 turns per level is intended or an error.
Page 69, Fire Trap: Duration is permanent until triggered.
Page 72, Hallucinatory Terrain: The spell should affect up to a 10' x 10' square area per caster level.
Page 77, Mind Blank: Duration should be 1 day.
Page 77, Mnemonic Enhancer: The AD&D version of this spell (Rary's Mnemonic Enhancer) has a duration of 1 day. It is unclear if the ALL duration of 2 turns per level is intended or an error.
Page 79, Phase Door: "If anyone is within the passage when it is dispelled, he is harmlessly ejected just as if he were inside a passwall effect." The description for Passwall on page 78 does not mention any such scenario.
Page 79, Polymorph Other: Duration is permanent until dispelled.
Page 79, Power Word Blind: This spell affects an area 30' in diameter.
Page 80, Prismatic Sphere: The sphere has a 20' diameter. Furthermore, the AD&D version of this spell is largely identical, except that the red and orange globes are negated by Cone of Cold and Gust of Wind, respectively, not Passwall and Fly as in ALL. It's unclear whether or not this change is intentional.
Page 82, Scribe: The -1 penalty for attempting to transcribe a spell three levels or more higher than the writer can cast should increase by one with each spell level beyond that (-2 at four levels higher, -3 at five, etc.).
Page 83, Simulacrum: The Simulacrum spell itself only creates a zombie-like being with 50%+1d10% of the original's hit points and 10%+1d4x10% of the original's class levels (if any). A further Reincarnation spell is required to give the simulacrum a vital force and personality. A Limited Wish spell is required to give it 35%+1d6x5% of the original's memories.
Page 83, Spell Resistance: The last sentence should read, "The caster may affect up to 1 creature per 4 levels of experience, with the duration divided evenly among them."
Page 83, Spider Climb: Unlike their AD&D counterparts, Labyrinth Lord spellcasters do not need to manipulate objects (material components) to cast spells. In light of this, Spider Climb's effect should not prohibit spellcasting.
Page 84, Stinking Cloud: Duration should be 1 round per level.
Page 85, Summon Familiar: Range should be 1 mile per level.
Page 86, Symbol: The cleric spell Restoration may also be used to remove the Symbol of Insanity's effect from a victim.
Page 91, Illusionist Spells: "Astral Spell" should read "Astral Projection."
Page 91, Magic-User Spells: Animal Growth is absent from the 5th level spell list.
Page 119, Aerial Servant: This creature can only be hit by magical weapons.
Page 120, Ankheg: Victims of the creature's acid spray are entitled to a saving throw for 1/2 damage.
Page 124, Boar: The giant boar varies considerably from its AD&D counterpart, which has 7 Hit Dice, a 3d6 damage attack, and a number encountered of 2d4. Furthermore, the AD&D warthog has 3 Hit Dice.
Page 125, Brownie: This creature saves as a 9th level cleric. In addition, the brownie itself also enjoys the same 18 DEX and immunity to surprise that it grants to a magic-user when serving as a familiar.
Page 125, Bulette: One of the monster's claw attacks is mistakenly listed at 2d6 damage instead of the correct 3d6.
Page 130, Babau: Hit Dice should be 7+14, not 7+10. This demon creates darkness in a radius of 5', not 10'.
Page 132, Marilith: Hit Dice should be 7+7, not 7+6.
Page 135, Vrock: This demon creates darkness in a radius of 5', not 10'.
Page 137, Bael: The reference to Alter Self should probably be to Doppelganger, the closest equivalent spell in ALL. Similarly, Produce Fire should be changed to Produce Flame.
Page 138, Erinyes: Hit Dice should be 6+6, not 6+5.
Page 140, Devil, Ice: This creature's mandible attack deals 2d4 damage, not 1d4. It may also use an Ice Storm once per day.
Page 141, Lemure: Damage should be 1d3, not 1d4.
Page 146, Dwarf, Duergar: These creatures are immune to all illusions and phantasms. Also, it is stated that they understand "the gesture language of the drow." There is no mention of this language in the main drow entry on page 149.
Page 150, Eel: The electric eel's bite should deal 1d3 damage, not 1d4. Additionally, this entry appears out of alphabetical order.
Page 154, Ghost: Partially materialized ghosts may only be hit by silver weapons (which deal 50% damage) or magical weapons.
Page 157, Golem, Clay: Once per day, the golem can act as if under the effect of a Haste spell for three rounds.
Page 160, Groaning Spirit (Banshee): This creature can only be hit by +1 or better magic weapons.
Page 162, Homonculus: The creature's bite should cause sleep for 5d6 minutes, not 5d6 turns. Converting this roll into turns multiplies the duration by a factor of ten! Additionally, AD&D states that a Mirror Image spell is required to create a homonculus, while ALL calls for an ESP spell instead.
Page 165, Lamia: Damage should be 1d4, not 1d6.
Page 165, Lammasu: These creatures may become invisible or transport themselves via Dimension Door at will.
Page 166, Lich: Hit Dice should be 11+, not 12+.
Page 172, Naga, Spirit: This creature casts spells as a 5th level magic-user and a 4th level cleric.
Page 172, Neanderthal: Damage should be 2d4 or weapon +1.
Page 173, Night Hag: These creatures are immune to sleep, charm, fear, fire, and cold-based spells, as well as weapons of less than +3 enchantment. They can use Gate to attempt to call a barbed devil or standard order demon with a 50% chance of success.
Page 177, Piercer: These creatures are 95% likely to surprise opponents.
Page 177, Pseudo-dragon: This creature's abilities as a familiar are not provided, despite a reference to such details in the Summon Familiar spell entry.
Page 178, Rakshasa: The reference to the illusionist spell Change Self should be to Doppelganger. Additionally, the creature's vulnerability to blessed crossbow bolts is not mentioned, although this may be a creative choice as opposed to an error.
Page 179, Remorhaz: Touching the creature's hide should result in 10d10 damage, not 1d10×100.
Page 187, Statue, Animate: The iron statue should have an Armor Class of 2, not 4.
Page 187, Stegosaurus: Both the creature's attacks should deal 2d8 damage.
Page 189, Titanothere: Trample damage should be 3d8, not 2d8.
Page 190, Treant: Morale should be 9, not 6.
Page 194, Wind Walker: A Slow spell deals damage to this creature as a Fire Ball.
Page 195, Wyvern: The sting causes 1d6 damage (plus poison), not 2d8.
Page 196, Xorn: These creatures surprise their opponents on a roll of 1-5 out of 6, not 1-3 out of 6. Furthermore, Xorn suffer 1d10+10 damage if a Passwall spell is cast upon them.
Page 196, Yellow Mold: Number encountered should be 1d8 (1d4), not 1d4 (1d8).
Page 206, Dragon Control: The chart used to determine the type of dragon controlled doesn't include the brass, bronze, copper, silver, or sea dragon types, only the ones listed in the Basic rulebook.
Page 206, Extra-Healing: Drinking this entire potion should restore 3d8+3 hp. Drinking 1/3rd of it should restore 1d8 hp.
Page 209, Spell Storing: The exact set of spells present in this ring initially is the only one it can ever hold, though they may be replenished.
Page 209, Telekinesis: Up to 200 pounds of weight can be moved by this ring's power.
Page 209, Scroll of Spells: As written, all spell scrolls contain either magic-user or cleric spells, with no provision made for druids (25% of cleric scrolls in AD&D were druidic) or illusionists (10% of magic-user scrolls in AD&D contained illusionist magic).
Page 212, Wand of Cold: The Cone of Cold deals 6d6 damage, not 3d6.
Page 213, Wand of Fire, Wand of Ice, Wand of Lightning: These wands are all designated as rechargeable. No method for magic item recharging is provided in the rules. This may be a deliberate omission rather than an error.
Page 214, Wand of Summoning: "This effect takes five segments to cast." This sentence should be disregarded altogether, as Labyrinth Lord does not divide its rounds up into segments. Also designated as rechargeable (see above).
Page 218, Cube of Force: The following spells and attacks also drain extra charges from the Cube: Catapult-like missiles (1), Fire Storm (3), Flame Strike (3), Prismatic Spray (7).
Page 221, Feather Token: The whip deals a base 1d6 damage (2-7 with the +1 bonus). It attacks independent of its owner as a 9th level fighter, similar to a dancing sword.
Page 221, Figurines of Wonderous Power: Each of the Ivory Goats may only be used three times before permanently losing its power.
Page 224, Horn of Blasting: The duration of deafness should be 1 turn, not 2d6 rounds.
Page 228, Rope of Strangulation: Victims are entitled to a saving throw versus spells to avoid being strangled.
Page 229, Talisman of Pure Good: A Chaotic cleric touching the talisman should also suffer damage.
Page 231, Sword +1, Flame Tongue: "Immune to fire" in sentence one should read "weak to fire." This error appears to be based on a misunderstanding of the term "inflammable" that appears in the DMG.
Page 232, Disruption Mace +1: Evil characters handling this weapon suffer 5d4 damage.
Page 238, Magic Research: "Spell casting classes may only create magic items usable by their class." This is clearly misleading as written, as it would preclude such commonly accepted practices as magic-users creating enchanted swords. The correct meaning could perhaps be better conveyed as "A spell caster may not create magic items that duplicate spell effects unique to other classes. For example, a magic-user could not create a Staff of Healing, nor a cleric a Wand of Fire Balls."
Pages 246 and 247, Sorrow of Brokenvale: The neanderthal stat blocks should list damage as 2d4 or weapon +1.
Page 261, Random Tavern Patron Traits: The second and third columns are swapped and should be transposed.
Page 263, Monster List: The giant boar should be listed in the HD 7 column. The lich should be listed in the HD 11 column.