Welcome! This is a guide to help explain the mechanics of rulesets, as well as to serve as a handy reference by providing descriptive details for the various rulesets that exist.
This post is an updated version of my Guide to Rulesets originally published here:
@byzantinist/splinterlands-a-guide-to-rulesets
Since then, there have been two new rulesets (Equalizer and Heavy Hitters) and several additional Untamed Legendary summoners have been introduced. I also correct information on how the number of rulesets and the Standard ruleset are determined. And the Reverse Speed section has been updated with the two new tiebreakers (rarity and monster level).
Each game has a 25% chance of having 1 ruleset and a 75% chance of having 2 rulesets. "Standard" is not the absence of a ruleset but is just one of the rulesets that might be randomly selected.
Currently, the rulesets do not factor in any tournament specifications. So Lost Legendaries (no legendary monsters allowed) has no real effect in an NL (no legendaries) tournament and Taking Sides (no neutral monsters allowed) has no real effect in an Alpha tournament since there are no neutral monsters in the Alpha set.
Rulesets are categorized into 3 types called Primary, Any, and Secondary.
If you have 1 ruleset, then any of the rulesets can be chosen.
However, if there are 2 rulesets, first the system will chose a ruleset that is either Primary or Any, and then it will choose a ruleset that is either Secondary or Any. That means that two Primary rulesets will not appear together (like Armored Up + Unprotected) and two Secondary rulesets will not appear together (most of which restrict your choice of monsters). A ruleset that is Any can appear with a Primary ruleset, a Secondary ruleset, or another Any ruleset.
Rulesets can be weighted to either increase or decrease their frequency.
Right now, all rulesets have the same frequency since the default weight is 1. If a ruleset has "weight":2, then it would appear twice as often.
In the past, certain rulesets were weighted higher. When new rulesets came out, they were often weighted with a higher frequency. And when there were balance concerns about Prince Rennyn, the Silenced Summoners, Healed Out, and Broken Arrows rulesets had higher than normal weights, which is something that some players like 
Normally, melee and ranged attacks have a miss chance if a slower monster is attacking a faster monster or if certain monster abilities are in play. Magic attacks always hit. A slower melee or ranged monster attacking a faster monster has a 10% miss chance for each difference in speed. And this miss chance is additive with the miss chance resulting from Dodge (25% miss chance), Flying (25% miss chance if the attacking monster is not flying), and Blindness (15% miss chance but Blindness doesn’t stack with itself). It is possible for one monster to have a 100% miss chance against another monster.
Under the Aim True ruleset, melee and ranged attacks automatically hit. That means speed does not factor into hit chance and the miss chance of Dodge, Flying, and Blindness is negated.
All monsters have an additional 2 armor. This is already factored in to the monster stats when you are selecting your team of monsters. This armor amount can be further impacted by abilities like Protect or Rust. The armor from Armored Up can be restored with Repair.
When you are selecting your team of monsters, you will see that all of their abilities are greyed out and do not apply.
Note that the Legendary Untamed summoner, Mimosa Nightshade, gives all of your monsters the Void ability and this does work in Back to Basics. Mimosa will also cast Affliction on all of your opponent’s monsters but since right now there is no way to heal in Back to Basics, the Affliction doesn’t do anything (except that in a Back to Basics + Earthquake game, Mimisa's Affliction will stop Chanseus' Triage from healing the back-line, thanks 
Similarly, Yodin Zaku's Blast ability works in Back to Basics while Chanseus the Great can use Repair, Triage, and Resurrection. However, Triage will only really help against Yodin Zaku's Blast since there are not any other ways to damage the back-line in Back to Basics.
Back to Basics is mutually exclusive with the Healed Out and Heavy Hitters rulesets.
When you are selecting your team of monsters, you will see that any that normally have Sneak or Snipe have those abilities greyed out since they do not apply.
The Opportunity and Reach abilities do work in the Fog of War ruleset. And if Fog of War is combined with Melee Mayhem, all melee monsters in the back-line can still attack the enemy tank.
If the enemy team has a monster with Taunt in the back-line, then your tank (and a second position melee monster with Reach) will target the enemy tank while your back-line monsters able to attack will target the monster with Taunt.
This negates all summoner abilities. When you are selecting your summoner, you will see that their abilities have been greyed out and do not apply.
Mimosa Nightshade’s Void and Affliction abilities are negated in Silenced Summoners. The same applies to Yodin Zaku's Blast and Chanseus the Great's Repair, Triage, and Resurrection.
The cost of the summoner still factors into your mana budget. And the level and rarity of your summoner still determine the highest level of monsters you can use in the battle.
(Nothing to add)
All melee monsters gain the Sneak ability, allowing them to attack the enemy monster in the last position. Remember that a monster with Sneak that is in the front position will attack the enemy tank.
If an enemy monster has Taunt, then your melee monsters in the back-line will target the monster with Taunt instead of the enemy monster in the last position.
Sneak takes precedence over Reach, Snipe, and Opportunity so the priority target will be the enemy monster in the last position.
Otherwise, if all of your monsters are melee in Super Sneak, then your tank will attack the enemy tank and the rest of your monsters will attack the enemy monster in the last position.
In the case of monsters with multiple forms of attacks, if a monster with magic + melee (like the Red Dragon) is in the first position then both attacks will be against the enemy tank. If the Red Dragon is in the back-line, then both attacks will target the enemy monster in the last position. If a monster with ranged + melee (like the Vigilator or War Chaang) is in the front position, it will only attack the enemy tank with melee since ranged cannot be used in the front position (though if the Close Range ruleset is also in play, then they can use both ranged and melee in the front and both will be against the enemy tank). If the Vigilator or War Chaang is in the back-line, then both attacks will target the enemy monster in the last position.
Super Sneak is mutually exclusive with the Melee Mayhem and Keep Your Distance rulesets.
All ranged and magic monsters gain the Snipe ability, which means they will target the first monster with a ranged attack, magic attack, or no attack that is in the back-line (i.e. not in the tank position). Monsters with two attack forms are eligible targets of Snipe. A monster with Snipe that is in the first position and is able to attack will target the enemy tank. But a monster with Snipe in the back-line will prioritize an eligible target in the second position instead of a ranged or magic monster in the tank position. If there are no enemy monsters with ranged attacks, magic attacks, or no attacks, all of the snipers will target the enemy tank by default.
If an enemy monster has Taunt, then all of your sniping or sneaking monsters in the back-line will target the monster with Taunt instead of their normal targets.
Since Sneak takes precedence over Snipe, if a monster has both abilities (e.g. Dragonling Bowman or Pyromaniac in a Target Practice game), it will attack the enemy monster in the last position.
All current Opportunity monsters have melee attacks so it is unknown whether Snipe or Opportunity has priority because it is not currently possible to have both.
In the case of monsters with multiple forms of attacks, this ruleset does not change how they function if they are in the front position (which normally allows magic and melee attacks but not ranged and the target is the enemy tank in all these cases). However, if a monster with multiple forms of attacks is in the back-line, they gain Snipe in this ruleset and will Snipe with their magic or ranged attack but they will not attack with their melee attack while in the back-line. One interesting exception is when Target Practice is combined with Melee Mayhem. In this case, a monster with two forms of attack will Snipe with ranged/magic and then their melee attack will be against the same back-line Snipe target instead of against the tank.
Target Practice is mutually exclusive with the Up Close & Personal ruleset.
Under this ruleset:
Summoners do not provide any armor. The abilities of Tyrus Paladium, the Peakrider, and the Drake of Arnak are greyed out and do not apply.
All monsters lose their armor. When selecting your team of monsters you will see that all monsters have already had their armor removed.
The Protect ability does not work and provides no armor.
Since there is no armor, Piercing, Repair (including Chanseus the Great's ability), Rust, Shatter, and the Wizard of Eastwood’s ability will not be useful.
Normally, magic bypasses armor. For melee and ranged attacks, they hit armor first and if the damage amount exceeds the armor, the excess is ignored (with the exception of Piercing attacks where the excess is then applied to health).
Under the Weak Magic ruleset, magic no longer bypasses armor so any magic attacks will hit armor first and if the magic damage exceeds the armor, the excess is ignored.
The Shield ability does not help against magic attacks. Void works normally and in that situation the reduced damage (after factoring in Void) gets applied to armor first.
There is currently no way for a monster with magic attacks to get Piercing.
Weak Magic is mutually exclusive with the Up Close & Personal and Lost Magic rulesets even though you can technically have a magic attack in Up Close & Personal with the Red Dragon.
Normally, monsters with ranged attacks can only use their ranged attacks in the back-line. A monster with a ranged attack in the front position cannot use that ranged attack (though a Vigilator or War Chaang can still use their melee attack when in the front position).
Under the Close Range ruleset, monsters in the front position can use their ranged attacks. A Vigilator or War Chaang will attack with both their ranged attack and their melee attack.
Close Range is mutually exclusive with the Broken Arrows and Up Close & Personal rulesets, even though you can technically have ranged attacks in Up Close & Personal with the Vigilator and War Chaang.
Since the 2 Earthquake damage is melee damage, Shield will reduce it to 1 damage while Void does not reduce it at all. Also, this melee damage applies to armor first so 1 point of armor will protect against the 2 earthquake damage.
A Flying monster who is hit with Snare loses Flying and will then take Earthquake damage from that point on. If the Snare is removed with Cleanse then it is Flying again and will not take Earthquake damage any more.
If Earthquake is combined with Back to Basics, then all monsters lose Flying so every monster will take 2 damage each round. Though if a hypothetical summoner granted Flying to all of their monsters that would still work in Back to Basics.
Right now, game effects happen sequentially and Earthquake damage does NOT happen simultaneously. For a given player, the earthquake damage is applied in sequence starting from the monster in the front position. The order that the damage is applied (and that monsters die) can be particularly relevant when monster abilities like Resurrect, Strengthen, and Protect are present.
Also note that right now all of the damage is applied to one player’s monsters and resolved before any damage is applied to the other player’s monsters. Suppose both players each have a single monster with the Weakness ability and 3 health at the end of the round (reduced to 2 health due to the other player’s Weakness). If Earthquake damage happened simultaneous, both monsters would die and it would be a draw. But right now, the damage is applied to one player first (this is randomly determined at the start, so it is essentially 50/50), which would kill their monster. The Weakness would then be removed from the other player’s monster so when Earthquake damage is applied to them, they would survive and win the battle.
In Equalizer, after both players have selected their teams, the initial health of all monsters is set to the highest base health of any selected monster (on either side). So if either player chose a Level 10 Peaceful Giant with 17 health, then all monsters start with 17 health.
This health can then be further modified by buffs and debuffs like summoners (Plado Emberstorm, Valnamor, Lyanna Natura, Prince Rennyn, Mother Khala, and Cryptmancer) and monster abilities (Strengthen and Weaken).
If I am playing with Prince Rennyn, Wood Nymph (with Strengthen), and Swamp Thing (with Weaken) and either of us selects a Level 10 Peaceful Giant, then all of my monsters will start with 19 health and all of your monsters will start with 16 health.
Monsters and summoners lose the Heal, Tank Heal, and Triage abilities. When you are selecting your team of monsters, you will see that any that normally have Heal, Tank Heal, or Triage have those abilities greyed out since they do not apply.
Repair is not considered healing and still functions under the Healed Out ruleset.
Life Leech is not considered healing and still functions as normal under the Healed Out ruleset, increasing the monster’s current and maximum health based on the amount of health that the enemy monster loses.
Since there is no healing, the Affliction ability will not be very useful.
Originally the wording of Healed Out only applied to monsters so it was theorized that a hypothetical summoner that gives a healing ability to your monsters would be able to provide healing in the Healed Out ruleset. But with the release of Chanseus the Great (who has Triage), Healed Out was reworded to also remove healing abilities from summoners, though there was a brief period when it was bugged so that Chanseus' Triage did work in Healed Out, though that was quickly fixed.
In Heavy Hitters, every monster gains the Knock Out ability, which means they deal double damage to monsters that are Stunned. A monster who already has the Knock Out ability does not get any additional benefit under this ruleset.
A monster with Oppress deals double damage to monsters with no attack. If a monster with Knockout and Oppress attacks a Stunned monster with no attack, it will deal quadruple damage (2 x 2 = 4).
Knock Out is mutually exclusive with the Back to Basics ruleset. Since Knock Out only does something against Stunned monsters, if there are no monsters with Stun being played then Knock Out will have no effect.
This also means that Knock Out will often have no impact on the game at lower league levels since there are fewer monsters with Stun.
Novice level Monsters with Stun:
Pit Ogre (Level 1)
Bronze level Monsters with Stun:
Medusa (Level 3) if used with an Epic summoner
Silver level Monsters with Stun:
Medusa (Level 3)
Spirit Shaman (Level 3)
Lord of Darkness (Level 2)
Lightning Dragon (Level 2)
Gold level Monsters with Stun:
Spark Pixies (Level 5)
Sniping Narwhal (Level 5)
Stone Golem (Level 5)
Dark Enchantress (Level 4)
Thunderbird (Level 4)
Bila the Radiant (Level 3)
Dragon Jumper (Level 3)
Goblin Mech (Level 6)
Gremlin Blaster (Level 5)
Cyclops (Level 6)
Dwarven Wizard (Level 4)
Diamond level Monsters with Stun:
Goblin Fireballer (Level 10)
Frost Giant (Level 4)
Undead Rexx (Level 9)
Soulstorm (Level 6)
Chain Golem (Level 4)
So at Novice level there is only a single monster in the game with Stun. That remains true at the Bronze level with the cornercase addition of a Level 3 Medusa used by an Epic summoner. When you advance to Silver league there are 5 monsters total with Stun. 16 total monsters at Gold league and 21 monsters at Diamond level.
#1. Normally, monsters take their turn based on speed. Faster monsters (with a higher speed stat) go first and if there is a tie, then the tiebreaker is based on the attack type. Monsters with a magic attack go first, then monsters with a ranged attack, and then all other monsters (melee attack monsters and monsters with no attack are in the same category). Recently, two additional tiebreakers were added. The next tiebreaker is rarity with Legendary monsters going first and then Epic, Rare, and Common monsters. If monsters are of the same rarity then higher level monsters will go first. If there is still a tie (meaning speed, attack type, rarity, and level are all the same) then it is random which monster goes first.
In Reverse Speed, monsters with a lower speed stat go first. And for the first tiebreaker based on attack type, melee attack and monsters with no attack go first, followed by ranged attack monsters, and then magic attack monsters. Common monsters will go before Rare monsters who go before Epic monsters who go before Legendary monsters. And lower level monsters will go before higher level monsters. If there is still a tie, then it remains random which monster goes first.
In Reverse Speed, the Red Dragon still attacks in the magic window while the Vigilator and War Chaang still attack in the ranged window. They do not attack during the window when melee monsters attack.
#2. Normally, slower monsters attacking a faster monster have a miss chance of 10% per difference in speed.
In Reverse Speed, faster monsters (with a higher speed stat) have a miss chance of 10% per difference in speed when attacking slower monsters (with a lower speed stat). Dodge, Flying, and Blindness function normally.
Most of the Secondary rulesets restrict your options for selecting monsters. If you are using the standard interface (e.g. a human using the Splinterlands website UI), then when selecting your team, your available options will be limited since the invalid monsters have already been filtered out.
However, if a player or a bot submits a team outside of the Splinterlands website UI which includes an invalid card, that may result in automatically losing the battle.
The Vigilator and War Chaang have a ranged attack (in addition to a melee attack) and therefore may not be selected.
0 is an even number so Furious Chickens are welcome in these games.
Contextual Background: “Evens Stevens” is a rhyming idiom. According to the Free Dictionary it means: 1. Having nothing due or owed on either side or 2. Having a tied score, as in a game.
Red Dragon, the Vigilator, and War Chaang have melee attacks (in addition to their ranged or magic attacks) and therefore may not be selected.
(Nothing to add)
While legendary monsters cannot be used, legendary summoners are still usable.
Red Dragon has a magic attack (in addition to a melee attack) and therefore may not be selected.
If an enemy monster has Taunt, then all of your melee monsters in the back-line will target the monster with Taunt instead of their normal targets.
If you have melee monsters in the back-line with Sneak or Opportunity, those abilities take precedence instead of attacking the enemy tank using the Melee Mayhem rules.
As mentioned in the Target Practice section, when Melee Mayhem is combined with Target Practice, a monster like Red Dragon, Vigilator, or War Chaang will first Snipe with their ranged/magic attack and then the melee attack will also be against that Snipe target and not against the enemy tank.
This is the only Secondary ruleset which is not a restriction on which monsters you can use. When I asked 
0 is NOT an odd number (it is even). No Furious Chickens for you!
Contextual Background: “Odd one out” is an idiom with alliteration. According to the Free Dictionary it means: 1. Someone who is excluded from or left out of a group for some reason or 2. Something or someone that is decidedly or markedly different, atypical, or unusual in comparison to others in a group.
The restriction to commons and rares only applies to monsters. You can still select epic and legendary summoners.
(Nothing to add)
While Broken Arrows, Keep Your Distance, and Lost Magic are exclusionary, Up Close & Personal is inclusive. Red Dragon, the Vigilator, and War Chaang have melee attacks (in addition to their ranged or magic attacks) and therefore they MAY be selected.
If you want to explore the source data for the rulesets, you can view it here:
