These ideas for new abilities for Splinterlands cards are compiled from ideas shared by the YGGSPL Alliance and comments posted by community members in the Splinterlands discord server.
If you have any suggestions for abilities to add to this, please post them in the comments!
Monster Abilities
Quicksand: Works like slow but changes based on the ruleset. Increases your opponent's speed for reverse speed or slows them in standard rules. Since we already have slow, this could have double the impact so -2 or +2 speed if we wanted to differentiate.
Confusion: A monster hit with confusion has a 50% chance of attacking a friendly monster.
Assail: Targets a monster with any healing ability. Currently tank-heal, self-heal, or triage.
Decay: Works like poison for armor. Reduces armor by 2 every round.
Plague: If any monster on the team is poisoned, the poison spreads to one monster each round.
Paralyze: A super-stun. A monster hit with paralyze cannot attack for the remainder of the battle unless cleansed.
Mimic: Replaces the monster in the tank position (with the mimic ability) with a copy of the opponent's tank monster. We envision this ability on a low-mana neutral monster.
Certainty: Works similar to inspire. All RNG abilities on friendly monsters have 100% chance to proc instead of 50% (poison, retaliate, etc).
Medic: Cleanses a back-line monster each round.
Edit: these next four were suggested by 
Vendetta: Every ranged unit has shatter.
Tungsten Tips: Resurrected units have enrage.
High Altitude: Fatigue starts from round 3.
Weakest Link: Every unit has the same speed as the slowest unit on the team.
Summoner Abilities
Supercharge: All monsters with the "recharge" ability start the battle "charged" and can attack during round one.
Scorn: Summoner can select one monster for which the rules do not apply. Such as one magic monster in the lost magic ruleset. Or a non-flying monster that is unaffected by earthquake. If this is too powerful it could be an ability on individual monsters.
7th Monster: Abiliy to summon a 7th monster in battle.
Items and Spells
Nullify: Silences the enemy summoner and removes all effects from the opponent's summoner. This could also be a spell from land.
Steal: All friendly monsters gain one ability from the enemy summoner. This could also be a spell from land.
Thank you to our alliance members and the greater Splinterlands community for many of these ideas.
The YGG Brawlers are part of a fantastic YGGSPL Alliance community. If you're looking for a Splinterlands guild, visit us on the YGGSPL Alliance Discord and the YGG Brawlers Discord.