Hi all. First off, really digging Arkham Horror. It's one of the first fully cooperative games that my gaming group has caught on to. I'm currently trying to introduce it to as many gaming communities around my area, so I decided to collect a database of Frequently Committed Errors (F.C.E) to help newer players, and veterans who may have missed a rule or two alike in order to streamline gameplay and ensure that people aren't making the game too hard (or easy) for themselves. Please let me know if any date I've collected so far is wrong (I don't want to be teaching people the wrong game) or if I've missed any crucial things. Any help to fill this list will be much appreciated.

Pre-Game Setup

Initial Campaign Deck Build
•   During initial deck building, all cards must have 0 white pips. Level 1 cards and above are not allowed.

Initial Deck Build
•   When creating the pool for basic weaknesses, only include cards from one core set and other expansions. Do not include any basic weaknesses from any second copy of core set or other expansions.
•   The Investigator knows the random basic weakness that is included in their deck. This is in case their weakness has the Permanent keyword.

Preparing the Encounter Deck
•   When setting up the encounter deck, if you have multiple core sets, only use cards from one core set.

Drawing your Starting Hands
•   During the Investigators initial draw, if a Weakness is revealed, it is set aside, and a new card is drawn, before the Weakness is returned back and reshuffled into the deck.
•   Starting with the Lead Investigator, each Investigator may take a mulligan, setting aside any number of the cards in their starting hand, before drawing back to a new set of 5. Any Weaknesses drawn this way are also set aside until you draw a hand size of 5 as normal, then all set aside cards are shuffled into the deck.

In-Game Flavor Order
•   During the start of the game, the Agenda is read before the Act.


Mythos Phase

Round Begins
•   The entire Mythos phase is skipped during the first round.

Check Doom Threshold
•   The Doom checker for the Agenda only occurs during this step of the Mythos phase. This means that the Agenda cannot advance during any other phase in the game unless specified otherwise.
•   Doom on all cards, like "Arcane Initiate", or "Cultist", are counted during the Doom check on the Mythos phase. They are removed if the agenda advances.
•   Excess Doom does not carry over to the next Agenda.

Investigators Draw 1 Encounter Card
•   Encounter cards are drawn and revealed one by one, rather than at the same time.
•   Encounter cards are drawn for every Investigator, not just the lead.
•   Any Investigator that draws a Encounter card with Peril cannot reveal or receive assistance from other Investigators.
•   Any Investigator that draws a Encounter card with Surge draws an additional card.
•   If an enemy Spawn location is not in play, the card is discarded. No new card is drawn to replace the discarded card.
•   Needs Confirmation: ***If an enemy Spawn location is unrevealed and in play, the enemy still spawns there.***


Investigation Phase

Investigator Order
•   The Investigators choose the order in which they go. The lead Investigator does not have to go first.

Activate
•   Assets are not exhausted unless the card states for it to occur.
•   Exhausted Assets can still be used for any ability that causes them not to be exhausted.
•   Any Assets with depleted uses are not automatically discarded.

Engage
•   Engaging an enemy may be used to pull enemies from other Investigators.
•   Investigators may Engage exhausted enemies.

Evade
•   You can only Evade enemies you are engaged with unless specified otherwise.

Investigate
•   Investigators can still Investigate even if there are no clues in a location. They will simply not pick up clues upon success.

Play an Asset or Event
•   Events that tell you to Evade or Fight a card do not pass automatically unless it states otherwise.

Fight
•   Investigators may Fight a disengaged enemy.
•   An exhausted enemy cannot Retaliate.
•   An enemy only Retaliates if the Investigator's attack misses.
•   If an attack against an enemy is failed, and that enemy is engaged with another Investigator, you deal Damage equal to your attack to the Investigator. The monster is not the one who damages the other Investigator.
•   Investigators may Fight exhausted enemies without engaging the target.

Attacks of Opportunity
•   Checking for attacks of opportunity only occurs when performing Actions. It does not happen during triggers or reactions.
•   When engaged with an enemy, performing an action avoids an attack of opportunity if Fight, Evade, Parley or Resign is performed during the action. This also applies for Asset, Events or any other activatable actions that were used to perform those tasks.
•   When engaged with an enemy, playing an Asset or Event avoids an attack of opportunity it has the Fast keyword.
•   When engaged with an Enemy, performing a Move action causes an attack of opportunity after the action cost is paid. After the attack of opportunity occurs, all engaged enemies in their threat area follow the Investigator into the new location.
•   An attack of opportunity happens after the costs for the action are paid for, but before the benefits and effects of the action occur.
•   Any action that costs multiple actions only provokes one attack of opportunity.

Other Actions
•   (Limit once per game.) refers to each Investigators ability to use the action. (Group Limit once per game.) may only be performed once for the group of Investigators.


Enemy Phase

Hunter Enemies Move
•   The Hunter keyword checks for equidistant Investigators. It does not favor a location with more Investigators.
•   Hunter enemies do not exhaust after they move. They may attack before they are exhausted.
•   Needs Confirmation: ***If an enemy is already in a space with an Investigator, and has both Hunter AND Prey, the enemy stays in the location due to the wording of Hunter, even if he has a more appealing Prey within range of his Hunter keyword.***

Enemy Attacks
•   If an Investigator is eliminated, all enemies disengage at once, and are not exhausted by the disengagement. If they were not previously exhausted, this will cause them to reengage other Investigators in their Location and perform their attacks.


Upkeep Phase

Investigators Check Hand Size
•   Investigators only discard down to their max hand size at the end of the upkeep phase. Investigators may have an excess of their maximum hand size during any other phase in the game.
•   Investigators may not choose to discard a weakness from their hand, unless a card specifically says otherwise.


Victory / Defeat

Awarding Experience
•   At the end of the game, Investigators only gain victory points from enemies that have a victory point value on them if they are in the victory display. Any enemies with a victory point value still in play award no experience.
•   At the end of the game, Investigators only gain victory points from locations that have a victory point value on them if they have no clues left on them.

Defeat
•   If all Investigators are eliminated, ‘no resolution was reached' conclusion occurs. In a campaign setting, the game is not over.


Universal Rules

Damage and Horror
•   Damage and horror can be assigned by the targeted Investigator to themselves and/or one or more of the Investigator's Assets in play. You do not need to choose only one target to assign all the damage and horror.
•   You cannot assign damage and horror to Assets if it were to cause that card to have damage or horror exceeding their maximum value.
•   Damage and horror are assigned at the same time, so assigning damage and horror can both be placed on an Asset even if one or both of the assignments would cause that Asset to be discarded.
•   Direct damage, or direct horror cannot be assigned to Assets.

Decision-making
•   When decisions must be made between two equally valid options, the lead Investigator chooses.

Doom
•   Discarded cards with Doom on them discard the Doom as well.

Drawing Cards
•   If the Investigator would ever draw from an empty deck, they shuffle their discard pile into a new deck, draw a card, then take one Horror.
•   When drawing a weakness card, you do not draw a card to replace it after its resolution.

The Grim Rule
•   The Grim Rule only applies if the options Investigators are unsure on how to resolve rules or during a timing conflict. This does not apply for obvious for decisions the lead Investigator may choose.

Investigator Elimination
•   Enemies engaged with an eliminated Investigator disengage at once, and are not exhausted by this disengagement. If they were not previously exhausted, this could cause them reengage other Investigators.
•   Eliminated Investigators drop all their clues in the location where they were eliminated.

Prey Keyword
•   Enemies with Prey do not switch who they are engaged with if a more favorable Prey enters their location. It only determines who they select when they automatically engage.
•   Prey breaks equidistant ties when checking where a Hunter enemy moves towards. It does not make a Hunter enemy chase its prey if it is further than the nearest Investigator.

Reactions
•   Investigators are not forced to use reactions.

Skill Tests
•   During skill tests, you need to match, not beat the displayed number.
•   During skill tests, the effect only happens once, regardless of how much you succeed by. Fight actions will always deal 1 damage, and a successful Investigation will always yield 1 clue unless it is specified otherwise.
•   Each Investigator can commit as many cards as they want during skill tests on themselves, and only up to one when assisting others in the same location as them.
•   All Skill cards must be committed before the chaos token is drawn.
•   The base value of a stat is the value printed on the card, before any modifiers from Skills or Assets.
•   Stat values below 0 are increased to 0. However, in skill tests, if the stat value is below zero and "Lucky!" is played, the +2 is applied to the initial negative value, not the 0 value.
•   If the Tentacle Chaos token is drawn, the Investigator automatically fails the test, even if shroud or the challenge is set to 0.

Trauma
•   Physical and mental trauma do not reduce your maximum health and sanity. After choosing Investigators in a scenario, they take damage and horror equal to their physical and mental trauma. Damage and horror taken this way may be healed during the scenario, but this does not remove the trauma.

Weaknesses
•   While in the Investigators decks, all Weaknesses are player cards. When they are drawn, their type may change. If they only have a Revelation effect, are placed in the Investigator's threat area, are Events or Assets, only the Investigator may encounter them. However, if they are Tasks, or are enemies, any Investigator may encounter them.


Specific Card Interactions

Skill Cards
•   The Investigator who commits "Guts" to a successful skill test draws the card, not the Investigator performing the skill test.
•   Max 1 committed per skill test refers to the limit all Investigators may play of the same named card. For example, Investigators can only commit 1 copy of "Guts" during a test, but may also commit 1 copy of "Unexpected Courage".

Other Cards
•   "Stray Cat", or "Cunning Distraction" can be used to Evade an enemy not engaged with the Investigator.
•   "Double or Nothing" causes the effect of a successful test to occur twice. It does not cause the test to succeed twice. This causes cards like "Dr. Milan Christopher" to trigger once, but cards like "Guts" and "Vicious Blow" to trigger twice.
•   If "Arcane Initiate" reveals a Weakness Spell card, you must draw it if there are no other Spells.
•   "Dynamite Blast" does not have a "Fight" effect. Therefore, it can provoke attacks of opportunity if you are engaged with any enemies.
•   "Cover Up!" does not take the clue tokens from the Location.
•   "Look what I Found!" can still be used on a Tentacle Chaos draw if Shroud is 2 or lower.
•   "Lucky!" cannot be used on a Tentacle Chaos draw.
•   "Elusive" disengages enemies. It does not exhaust them.

Note: I have two notes there that state "Needs Confirmation" as I assume this is how the game works, but I couldn't seem to find confirmation anywhere.