Having looked through the original article, the WotC article that discusses the format and the various threads on these forums about the format, I can't help but conclude that there exists no definite set of rules for playing Horde in EDH. Everyone appears to be coming up with their own sets of main rules and house rules, which works to some extend, but does not exactly provide many resources for newcomers or any consistency when it comes to niche cases. Therefore, it might be helpful to make a thread where everyone can discuss and collect rules that have proven to be helpful.
In order to get the discussion rolling, I will start off with a set of rules for playing Horde in EDH, based on the rules of the original article, random other thoughts I have read and personal musings. When designing rules, I will focus on two major principles:
Principle 1: The rules should cover as many potential circumstances as possible and allow for the largest possible card base to create Horde decks from. Due to the nature of the format, complete inclusion will likely not be possible, but we should at least make an attempt to create rules, rather than immediately stating: "Just don't use these cards."
Principle 2: The randomness of Magic is inherent in the unknown factor of the which cards will be drawn at any given time. Therefore, it is best that the Horde not devolve into a series of dice rolls. On the other hand, having the players play the enemy creates a conflict of interest, since you are attempting to outsmart yourself. Therefore, there should be fixed rules governing the Horde's behavior that make it reasonably smart, but to some extend predictable, allowing players to attempt to outsmart it.
Basic Rules:
The players play cooperatively against the Horde deck, following 2-headed Giant rules.
The players share life totals. 30 life per player should be enough against tougher decks.
The Horde deck plays itself. It reveals cards and automatically plays them.
The objective is to survive against the Horde deck until the Horde library is exhausted and there are no more Horde creatures on the battlefield.
The players take three turns at the beginning and then alternate with the Horde deck.
Dealing Damage to the Horde causes it to mill that many cards.
Horde Deck Design:
Size: Given the power that the average EDH deck can field, it should probably be larger than the stated 100 cards of the original article. A total of 200 seems appropriate, adjusted by removing a certain number of cards at random if there are fewer than 4 players (which is the default assumption). The size should depend on the needs of the individual playgroup, though. A larger Horde is more difficult and makes for longer games.
Composition: The Horde deck consists of tokens and regular cards. The recommended ratio appears to be around 50%-60% Tokens / 40%-50% Regular cards. The exact ratio is up to the needs of the individual group. Generally speaking, the higher the token ratio, the more explosive the Horde deck becomes and the harder it is to fight.
Choice of Cards: The power level of the cards used should be adjusted to meet the needs of the playgroup. Things to keep in mind are that the Horde does not need to pay mana for its spells and is assumed to have infinite mana. Therefore, the power of the deck is directly a function of the raw power of each card, regardless of mana cost. A deck filled with nothing but Plague Wind and Eldrazi Titans may be too harsh. Likewise, be wary of any cards with X costs or activated abilities that cost mana.
As for the tokens, the original proposed deck consisted of mostly 2/2 zombies and a handful of 5/5 zombies for sudden unexpected spikes. You can put any variety of tokens in the Horde deck that will fit the theme, but keep in mind that they can unexpectedly appear in large numbers in a single turn. A Horde of 4/4 angels or 5/5 dragons may be too much to handle for most groups.
The phases of the Horde's Turn:
Untap: As normal.
Upkeep: As normal. Either the Horde's own permanents or those of the players can cause upkeep triggers.
Reveal: The Horde reveals the top card of its library. If this card is a token, then another card is revealed. This process repeats until a non-token card is revealed.
Main phase: There are three things that happen in the main phase in this particular order.
1) The revealed tokens are put on the battlefield. These are not spells and can therefore not be countered. Then the revealed non-token card resolves, which does count as a spell. If this card is a spell that cannot be cast due to the absence of a legal target or if the spell is harmful and the only legal targets are in the Horde itself, then it is placed in the Horde's hand.
2) Any tokens in the Horde's hand are put on the battlefield (again, not spells). Then the Horde attempts to cast any spells in its hand. If a spell cannot be cast due to the absence of a legal target or the spell is harmful and the only legal targets are in the Horde itself, then it remains in the hand and the attempts will continue in subsequent turns.
3) The horde activates any activated abilities of its permanents that require tapping or are for some reason single-use or restricted to sorcery speed. If an activated ability cannot be used due to the absence of a legal target, then no attempt is made. Equipment is also equipped at this stage and non-permanent based abilities like Unearth or Flashback are activated.
Combat Phase: All creatures that the Horde controls have haste and attack if able. More on the nature of Horde attacks later.
End Phase: Any "Until End of Turn" effects end. The Horde discards down to seven cards (although the Horde should not have this many cards in hand under normal circumstances).
The Horde's decision making:
Two things should be done to make this flow smoothly. First, the Horde permanents should be placed from left to right in the order that they were put on the battlefield. This is to keep track of which permanent was there the longest.
Second, before the game starts, the players should decide to give each of them a number, going from 1 to however many players there are. This represents who is at the front line and who is hanging back.
Whenever the Horde is required to either target or choose one of its own permanents, it chooses based on a FIFO (first in, first out) system. This made the most sense in terms of flavor. The zombie who runs at the front (i.e. has been on the battlefield the longest) will be the first to pick up the pointy stick, but also the first to take a shotgun blast.
Whenever the Horde is required to target a permanent of the opponent, they will choose whichever legal target has the highest CMC. If two or more targets are tied, they determine based on FIFO. The Horde goes for whatever seems to be the biggest and shiniest thing.
Whenever the Horde is required to target something in any graveyard, they will choose whichever legal target has the highest CMC. If two or more targets are tied, then it chooses whichever is closest to the top of its graveyard (if they are still tied, choose at random).
Whenever the Horde has to target a player directly, they will target Player 1. If this player is an illegal target or more targets are required, they will then target Player 2, etc. Generally speaking, though, the Horde will likely not carry many spells that target players directly, other than to deal damage or cause life loss.
When the Horde attacks, the oldest (leftmost) creature attacks player number 1. The next oldest creature attacks player 2, etc. etc. If there are four players and a fifth creature attacks, then the loop starts again and that creature attacks player 1. Most of the time, this is not relevant, since life totals and defenders are shared, but it can matter for effects such as Hypnotic Specter or players attempting to defend themselves with cards like Circle of Protection: Black.
If a Planeswalker is summoned, that Planeswalker temporarily becomes Player 1 (all other player numbers move down by one) and is attacked as appropriate. A subsequent Planeswalker would become Player 2, etc.
The Horde has infinite mana and will always pay any additional mana costs for any spells or abilities. This includes costs like Kicker and Overload.
If an activated ability does not require tapping or pose any other restrictions, then the Horde will use its infinite mana to activate it as early and as often as possible with as many targets as possible. This basically means that creatures with Regenerate have to be destroyed by means that do not allow for regeneration and a creature like Onyx Mage basically reads: "All creatures you control have Deathtouch.
[OPTIONAL]Some creatures with activated abilities based on mana could be houseruled to also have a tapping requirement.
Any decision made by the Horde that is not covered here is resolved as randomly as possible.
Special rules governing the Horde:
The tokens that are part of the deck itself can go in the graveyard or hand and are not subject to the usual rules governing tokens that dictate that they fade from existence when leaving the battlefield. Tokens generated by spells or permanents, however, function as normal.
The tokens are not considered "cards" for the purpose of cards such as Eradicate or Bribery. They are, however, counted if an effect asks for the number of cards in the library or to reveal a number of cards.
If the Horde gains any amount of life, it instead takes that many cards from the top of its graveyard and puts them on the bottom of its library. If the graveyard is empty, life gain has no effect.
The Horde has a hand, but usually, it is empty. Cards can end up there in three ways. 1) An effect returned a permanent of the Horde to its owner's hand. 2) A spell or permanent caused the Horde to draw cards. 3) The Horde revealed a spell that could not be cast due to the lack of viable targets. If the Horde has a hand, it can be targeted with discard spells as normal. Abilities like Hellbend work as normal, checking the Horde's hand.
The Horde is not required to cast a harmful spell if the only legal targets are its own permanents (the spell instead goes to its hand). However, if a spell requires multiple targets and the players have some legal targets but not enough, then the Horde will target its own permanents to make up for the difference if this allows the spell to be cast (this rule refers to effects like Hex or Decimate).
Attempting to mill the Horde is a viable strategy. However, any of the grind effects (such as Mind Funeral) will check for non-token cards instead of land. This is to prevent incredibly easy one-shot victories.
Banned list:
This pertains to the player's decks. There are cards that the designer of the Horde deck obviously shouldn't be using (Soul Burn comes to mind), but since no one is seeking to win games for himself with a Horde deck, the group can figure out on their own what works or not. The following is just a list of cards that can make victory against a Horde utterly trivial.
During the main phase, I have the horde check their graveyard for flashback and unearth cards. I assume you do that too, and just forgot to write it down.
Adding life per player is good if you want to change the deck size for the number of players, but counting out 50 cards gets annoying, and if you want to shuffle in the cards you removed again, it requires more counting. It's also fun to just fight the whole horde all the time. For this reason, I have the life total start at 60 for any number of players. Also, 40 life per player seems like a lot. A 4 player team would have 160 life.
I like the rules for targetting that you have. They seem really complicated, but it's really just 'the horde does this' once you know how it works with each card in the deck. Also, it is best if you design your horde deck with the fewest possible targetted abilities and spells, unless it is easy to factor in like boneknitter's regeneration (all zombies always have a regeneration shield).
I did mention Unearth in the Main Phase, section 3) part, but forgot to mention Flashback there. I'll add it in.
I deliberately avoided stating specific life totals and deck sizes, since I found in the past that different groups of EDH players have very different power levels in their metagame. I merely took the highest numbers as examples, but you're right that 40 life per players is probably overdone. 30 life per player should be the maximum against even a tough deck, but it depends on which tokens you want to throw in. If you make the total too low, then a good flip of the right tokens on turn 3 can end the game in no time.
If the deck designer finds remembering the rules for targeting cumbersome, then he or she can just take out the targeted abilities. However, I wanted rules that will at least cover them so that they have the option. I found that always going for the highest CMC made most sense flavorwise (the Horde rampages automatically towards the biggest, shiniest thing) and usually, it means they'll also snipe one of the best permanents. However, smart players can also use this to throw out a Kindercatch to distract the Horde from their Baneslayer Angel.
Ya, that makes sense. I took out pretty much all the targetted stuff in my deck because it just makes the game much smoother.
Maybe for the rules for life total though, since it would be nice to have rules that everyone can follow, you can factor in life total adjustments for the sake of difficulty (add life if it's too hard, take it away if it's too easy).
For my own deck, I use 60 life (as I stated above), and adjust the amount of turns the players get in order to modify the difficulty.
Having looked through the original article, the WotC article that discusses the format and the various threads on these forums about the format, I can't help but conclude that there exists no definite set of rules for playing Horde in EDH. Everyone appears to be coming up with their own sets of main rules and house rules, which works to some extend, but does not exactly provide many resources for newcomers or any consistency when it comes to niche cases. Therefore, it might be helpful to make a thread where everyone can discuss and collect rules that have proven to be helpful.
In order to get the discussion rolling, I will start off with a set of rules for playing Horde in EDH, based on the rules of the original article, random other thoughts I have read and personal musings. When designing rules, I will focus on two major principles:
Principle 1: The rules should cover as many potential circumstances as possible and allow for the largest possible card base to create Horde decks from. Due to the nature of the format, complete inclusion will likely not be possible, but we should at least make an attempt to create rules, rather than immediately stating: "Just don't use these cards."
Principle 2: The randomness of Magic is inherent in the unknown factor of the which cards will be drawn at any given time. Therefore, it is best that the Horde not devolve into a series of dice rolls. On the other hand, having the players play the enemy creates a conflict of interest, since you are attempting to outsmart yourself. Therefore, there should be fixed rules governing the Horde's behavior that make it reasonably smart, but to some extend predictable, allowing players to attempt to outsmart it.
Basic Rules:
Horde Deck Design:
Size: Given the power that the average EDH deck can field, it should probably be larger than the stated 100 cards of the original article. A total of 200 seems appropriate, adjusted by removing a certain number of cards at random if there are fewer than 4 players (which is the default assumption). The size should depend on the needs of the individual playgroup, though. A larger Horde is more difficult and makes for longer games.
Composition: The Horde deck consists of tokens and regular cards. The recommended ratio appears to be around 50%-60% Tokens / 40%-50% Regular cards. The exact ratio is up to the needs of the individual group. Generally speaking, the higher the token ratio, the more explosive the Horde deck becomes and the harder it is to fight.
Choice of Cards: The power level of the cards used should be adjusted to meet the needs of the playgroup. Things to keep in mind are that the Horde does not need to pay mana for its spells and is assumed to have infinite mana. Therefore, the power of the deck is directly a function of the raw power of each card, regardless of mana cost. A deck filled with nothing but Plague Wind and Eldrazi Titans may be too harsh. Likewise, be wary of any cards with X costs or activated abilities that cost mana.
As for the tokens, the original proposed deck consisted of mostly 2/2 zombies and a handful of 5/5 zombies for sudden unexpected spikes. You can put any variety of tokens in the Horde deck that will fit the theme, but keep in mind that they can unexpectedly appear in large numbers in a single turn. A Horde of 4/4 angels or 5/5 dragons may be too much to handle for most groups.
The phases of the Horde's Turn:
Untap: As normal.
Upkeep: As normal. Either the Horde's own permanents or those of the players can cause upkeep triggers.
Reveal: The Horde reveals the top card of its library. If this card is a token, then another card is revealed. This process repeats until a non-token card is revealed.
Main phase: There are three things that happen in the main phase in this particular order.
1) The revealed tokens are put on the battlefield. These are not spells and can therefore not be countered. Then the revealed non-token card resolves, which does count as a spell. If this card is a spell that cannot be cast due to the absence of a legal target or if the spell is harmful and the only legal targets are in the Horde itself, then it is placed in the Horde's hand.
2) Any tokens in the Horde's hand are put on the battlefield (again, not spells). Then the Horde attempts to cast any spells in its hand. If a spell cannot be cast due to the absence of a legal target or the spell is harmful and the only legal targets are in the Horde itself, then it remains in the hand and the attempts will continue in subsequent turns.
3) The horde activates any activated abilities of its permanents that require tapping or are for some reason single-use or restricted to sorcery speed. If an activated ability cannot be used due to the absence of a legal target, then no attempt is made. Equipment is also equipped at this stage and non-permanent based abilities like Unearth or Flashback are activated.
Combat Phase: All creatures that the Horde controls have haste and attack if able. More on the nature of Horde attacks later.
End Phase: Any "Until End of Turn" effects end. The Horde discards down to seven cards (although the Horde should not have this many cards in hand under normal circumstances).
The Horde's decision making:
Two things should be done to make this flow smoothly. First, the Horde permanents should be placed from left to right in the order that they were put on the battlefield. This is to keep track of which permanent was there the longest.
Second, before the game starts, the players should decide to give each of them a number, going from 1 to however many players there are. This represents who is at the front line and who is hanging back.
Special rules governing the Horde:
Banned list:
This pertains to the player's decks. There are cards that the designer of the Horde deck obviously shouldn't be using (Soul Burn comes to mind), but since no one is seeking to win games for himself with a Horde deck, the group can figure out on their own what works or not. The following is just a list of cards that can make victory against a Horde utterly trivial.
Moat
Magus of the Moat
Powerstone Minefield
Aether Flash
Lightmine Field
Meishin, the Mind Cage
Silent Arbiter
Dueling Grounds
Spreading Plague
During the main phase, I have the horde check their graveyard for flashback and unearth cards. I assume you do that too, and just forgot to write it down.
Adding life per player is good if you want to change the deck size for the number of players, but counting out 50 cards gets annoying, and if you want to shuffle in the cards you removed again, it requires more counting. It's also fun to just fight the whole horde all the time. For this reason, I have the life total start at 60 for any number of players. Also, 40 life per player seems like a lot. A 4 player team would have 160 life.
I like the rules for targetting that you have. They seem really complicated, but it's really just 'the horde does this' once you know how it works with each card in the deck. Also, it is best if you design your horde deck with the fewest possible targetted abilities and spells, unless it is easy to factor in like boneknitter's regeneration (all zombies always have a regeneration shield).
BBB Two Hundred Zombies BBB
Duel Commander
WR Tajic, Wrath of the Manlands RW
BGW Doran Destruction WGB
Commander
GUB Mimeoplasm, Screw Politics BUG
BR Mogis, God of Slaughter RB
RGW Marath, Ramp and Removal WGR
WUBRG Karona, Jank God GRBUW
I deliberately avoided stating specific life totals and deck sizes, since I found in the past that different groups of EDH players have very different power levels in their metagame. I merely took the highest numbers as examples, but you're right that 40 life per players is probably overdone. 30 life per player should be the maximum against even a tough deck, but it depends on which tokens you want to throw in. If you make the total too low, then a good flip of the right tokens on turn 3 can end the game in no time.
If the deck designer finds remembering the rules for targeting cumbersome, then he or she can just take out the targeted abilities. However, I wanted rules that will at least cover them so that they have the option. I found that always going for the highest CMC made most sense flavorwise (the Horde rampages automatically towards the biggest, shiniest thing) and usually, it means they'll also snipe one of the best permanents. However, smart players can also use this to throw out a Kindercatch to distract the Horde from their Baneslayer Angel.
Maybe for the rules for life total though, since it would be nice to have rules that everyone can follow, you can factor in life total adjustments for the sake of difficulty (add life if it's too hard, take it away if it's too easy).
For my own deck, I use 60 life (as I stated above), and adjust the amount of turns the players get in order to modify the difficulty.
BBB Two Hundred Zombies BBB
Duel Commander
WR Tajic, Wrath of the Manlands RW
BGW Doran Destruction WGB
Commander
GUB Mimeoplasm, Screw Politics BUG
BR Mogis, God of Slaughter RB
RGW Marath, Ramp and Removal WGR
WUBRG Karona, Jank God GRBUW