I just came up with this. I tried to only include game essentials for understanding how to control one's investigator. Secondary strategies and details that will rapidly become obvious were omitted. It presumes that an experienced player will be present and handling the mythos deck and the first player token (or you can just completely ignore phase order the first game, which might actually be a better idea and make things go faster albeit more chaotically, but much less boringly, just get ready to drill people into order by game two or three). Rules minutiae can be discovered over time and explained on the occasions that they arise.
It's intended to basically rush a player into the equivalent of a couple years of gaming experience in a game or two. Hopefully if people read this two or three times before the game and keep a copy at hand, the game explanation won't be perplexing and overwhelming.
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Time: The more time that passes, the worse things will get, and horrible events will occur. The faster you play, the more likely you are to win. Arkham punishes exploration and other digressions from the primary objective with exponentially increasing pain and ultimately death.
The primary objective, winning: The main way to win the game is collecting thirty clues or clue equivalents and spending them to close and seal gates.
Clues: sets of five clues can be used to close and seal gates. Once six gates are sealed, the game is won. Clues can not be traded so don’t take more than you can need for sealing (5 per gate) or other players won’t be able to get enough.
Gates: Most turns of the game, a gate appears on a location and monsters emerge from it. Players can enter gates, spend two turns inside them, then return from them and close them by rolling a successful skill check against them. Inside gates, you can’t read tomes.
Success: a die roll of 5 or 6.
Skill check: players have 6 basic types of skill checks. Speed, sneak, fight, will, lore, and luck checks. Cards will tell them to make a speed, sneak, fight, etc. check of +1, +0, -1, -2, etc. This means look at their skill number and add or subtract the number mentioned on the card from it and roll that many dice. If one of those dice is a success, the skill check is passed. I.e. if a card says make a +3 speed check and you have 4 speed, roll 7 dice.
Special skill checks: Spell checks are a type of lore check that determines whether or not a spell you cast has any effect. Evade checks are a type of sneak check made with the number on the front of monster card (if passed, you run away from the monster, if failed, the monster attacks you). Horror checks are a type of will check made against the blue number on the back of the card at the beginning of combat. If it is passed or failed, it is not repeated. Failure results in sanity loss equal to the number of blue dots under it. Combat checks are a type of fight check made against the red number on the back of the monster card. Failure results in stamina loss equal to the number of red hearts under it. To defeat the monster and take it as a trophy (a token that can be traded a certain locations) you must roll successes equal to the number of blood drops on its bottom middle. Up to two hands of weapons or spells can add bonuses to the number of dice rolled for your combat checks. Each time you fail to defeat the monster, if you still have stamina, you must try again, or try to run from it. Generally speaking, sanity is easier to lose than stamina— you need to protect it more.
Special Monster abilities:
Endless-this monster can not be taken as a trophy.
Resistance-this will reduce your weapons’ dice bonus in half, rounded up.
Immunity-this will eliminate your weapons’ bonus entirely.
Nightmarish X-this monster will cause X sanity damage if you pass its horror check.
Overwhelming X- this monster will cause X stamina damage if you defeat it.
Primary Locations for trading trophies in order of usefulness: Science Building (clues), Ma’s Boarding House (Allies), South Church (Blessing— this temporary effect makes dice a success on rolls of 4 also), The Police Station (an item that allows teleportation across the board).
Crucial locations: The Newspaper (where you are most likely to get money in the form of retainers which give $2 a turn). The Curiosity Shop (where money is most effectively spent), and The Bank (where money is most easily made, if you’re desperate).
What happens if you lose all your sanity or stamina: for stamina, draw an injury, get all your stamina back, move to the hospital and lose a turn, for sanity, draw a madness, get all your sanity back, move to the asylum and lose a turn. Lose your retainer too.
Crucial Items: Elder Signs (equivalent to 5 clue tokens), and King in Yellow (equivalent to 4 clue tokens), both are found in the unique item deck (at the Curiosity Shop).
Crucial Strategy: clues can not be traded, so players should generally not collect more than five (since that is all that is needed for closing and sealing a gate). Risk management strategies are successful in the game. It is important that characters holding multiple clues play as safely as possible so they do not waste this vital resource by dying, having their time stolen, or becoming crippled.
This is a team game: The game is a team effort, it is important that everyone become a Socialist for the duration of the game. Self-aggrandizement will lead to collective defeat. Players with clues are the most important to protect by sharing resources so monsters can not defeat them. Weaker characters should support stronger characters. Characters that need to perform a task should be supported by other characters. Normally, at most, two players should be concentrating on gathering clues while other players are performing other tasks (going to close and seal gates, shopping, trading for resources, and last and least important, though most fun, hunting monsters).
Closing and Sealing Gates: this requires a successful fight or lore check made using the number on the gate after they have been exited. Again, seal 6, and you win.
Gate Frequency: not all locations open gates at the same frequency, the higher frequency they are, the more monsters they tend to produce (consequently it is a higher priority to close and seal them). If too many gates are open, the game is usually lost.
High Frequency Gate Locations: The Woods, Unvisited Isle, Independence Square, The Witch House
Medium Frequency Gate Locations: Black Cave, Graveyard, The Unnameable
Low Frequency Gate Locations: Once or twice per game if there are too many gates on the board, you can close these without sealing them (i.e. without spending 5 clue tokens). This will prevent you from losing from too many gates being open, but it will not get you closer to winning by sealing 6 gates. The locations are Hibbs Roadhouse, The Historical Society, The Silver Twilight Lodge, The Science Building, Y’ha-nthlei (ultra-rare), and Devil’s Hopyard. It is safe to let 3 or sometimes even 4 clues accumulate there since gates rarely appear in these places. When a gate appears on a location, it destroys all clues there. On average, less than one clue is generated per turn and games last ten to twenty turns, so it is important to not waste clues (since thirty are needed) and to find other means of gaining clues and clue equivalent items. Act as if gates not specified here are high frequency gates.
Good luck: No, really, have your luck skill at its maximum unless you need lore for spells. You tend to have about 3 luck checks for every 2 lore checks. Although there are a few locations that violate this rule (e.g. The Witch House, The Library, and The Administration Building).
Turn order: In the first part of your turn you can adjust your skills by changing them by a number equal to your focus (if you have focus 1, you can change your skills by 1, 2 by 2, or 3 by 3). This part of your turn is called upkeep. Adjust your skills so they fit what you think you will need to do that turn and the turn after. If you have very low focus, you need to plan for three turns ahead. Then comes movement (you can move a number of spaces equal to your speed if you are on the same space as someone else during this part of the turn you can trade almost anything with them except allies, skills, injuries, madnesses, clues, blessings, and retainers. If you move onto a space with a monster, or start movement with a monster on your space, you must run away from it (pass an evade check) or end your movement phase and fight/evade it and all other monsters on the space.
If further details are desired prior to the game, go here and consult the manual.
http://www.arkhamhorrorwiki.com/Main_Page
http://new.fantasyflightgames.com/ffg_content/Arkham_Horror/AH_Rules_internat.pdf
(I know you crave for it
). Not even mentioning final combat sets up the right mindframe.