Splinterlands (aka Steem Monsters) has 21 unique battle rulesets. However, as far as I know, there's no list of rulesets. Until now. Here they are:
No modification to the standard gameplay rules and mechanics.
Legendary Monsters may not be used in battles.
Monsters lose all abilities.
Monsters with Melee attack can attack from any position.
Neutral Monsters may not be used in battles.
Summoners do not give any stat buffs or debuffs.
Only Common and Rare Monsters may be used in battles.
Melee and Ranged attacks always hit their target.
All Monsters with Melee attack have the Sneak ability.
Magic attacks hit Armor before reducing Health.
Monsters do not have any armor and do not get armor from Abilities or Summoner Buffs.
All Monsters with Ranged or Magic attack have the Snipe ability.
Only Monsters with Melee attack may be used in battles.
Monsters with the lowest Speed attack first and have the highest chance of evading attacks.
Monsters with Ranged attack may not be used in battles.
Monsters lose the Sneak and Snipe abilities.
Only Monsters & Summoners that cost 4 Mana or less may be used in battles.
Non-flying Monsters take 2 Melee damage at the end of each round.
All healing abilities are removed from Monsters.
All Monsters have 2 Armor in addition to their normal Armor stat.
Monsters with Melee attack may not be used in battles.