Being new to Splinterlands means having rule sets reference abilities that I haven't gotten completely down yet. I tried finding a complete list of all abilities in the game without any luck, so I decided to make one.
Weaken: Reduces the health of all enemy monsters. (1)
Flying: Has an increased chance of evading melee or ranged attacks from monsters who do not have the flying ability. (25%)
Reach: Melee attack monsters with the reach ability may attack from the second position of the team.
Sneak: Targets the last monster on the enemy team instead of the first monster.
Snipe: Targets enemy monsters with ranged, magic, or no attack that are not in the first position.
Opportunity: Monsters with the opportunity ability may attack from any position and will target the enemy monster with the lowest health.
Shatter: Target's armor is destroyed when hit by an attack from monsters with shatter.
Shield: Reduced damage from melee and ranged attacks. (1)
Stun: When a monster with stun hits a target, it has a chance to stun the target causing it to skip its next turn.
Heal: Restores a portion of the monster's health each round.
Blast: Deals additional damage to monsters adjacent to the target monster.
Last Stand: gains increased stats if it's the only monster on the team alive.
Tank Heal: Restores a portion of the monster in the first position's health each round.
Void Armor: Magic attacks hit this monster's armor before its health.
Inspire: Gives all friendly monsters +1 melee attack.
Headwinds: Reduces the ranged attack of all enemy monsters.
Dodge: Has an increase chance of evading melee or ranged attacks. (25%)
Void: Reduces damage from magic attacks.
Magic Reflect: When hit with magic damage, does reduced magic damage back to the attacker.
Retaliate: When hit with a melee attack, monsters with retaliate have a chance of attacking their attacker.
Silence: Reduces the magic attack of all enemy monsters.
Return Fire: When hit with a ranged attack, monsters with return fire will return reduced damage back to their attacker.
Swiftness: All friendly monsters have increased speed.
Demoralize: Reduces the melee attack of all enemy monsters.
Protect: All friendly monsters gain +2 armor.
Taunt: All enemy monsters target this monster (if they are able to).
Snare: When attacking enemies with flying, removes the flying ability and cannot miss.
Immunity: The monster is immune to negative status effects.
Thorns: When hit with a melee attack, does damage back to the attacker.
Scavenge: Gains 1 mas health each time any monster dies.
Halving: Each time this monster hits a target, the target's attack is cut in half (rounded down).
Slow: Reduces the speed of all enemy monsters.
Double Strike: Monster attacks twice each round.
Resurrect: When a friendly monster dies it is brought back to life with 1 health.
This can only trigger once per battle.
Strengthen: All friendly monsters have increased health.
Close Range: Monsters with close range ability can perform ranged attacks from the first position.
Life Leech: Monsters health increases each time it damages an enemy monster's health in proportion to the damage dealt.
Divine Shield: The first time the monster takes damage it is ignored.
Piercing: If melee or ranged attack damage is in excess of the target's armor, the remainder will damage the target's health.
Affliction: When a monster with affliction hits a target, it has a chance of applying affliction on the target causing it to be unable to be healed.
True Strike: This monster's attacks cannot miss.
Cleanse: Removes all negative effects on the monster in the first position on the friendly team.
Repair: Restores some armor to the friendly monster whose armor has taken the most damage.
Enrage: Has increased melee attack and speed when damaged.
Cripple: Each time an enemy is hit by a monster with cripple it loses one max health.
Oppress: Does double damage when attacking an enemy that has no attack.
Hopefully this will be helpful! Let me know if you notice any errors, or if you'd like me to add anything relevant for an ability. I know getting the wiki updated is in the works, so I think I'll go ahead and transfer this to there in the next few days once I find some time.