Hello there!
I thought I’d give my two cents as well on new possible abilities for troops:
- Deviation: a troop with this ability can choose who will be the “skull” target (might be for a limited number of turns). For instance, if my opponent has a Gorgotha on top and a Silencer second, I might use my troop with Deviation so that any skull I match would target Silencer instead.
- Power-driven: a creature that is power-driven will gain 1 magic every time after casting a spell, but will also see an increase in mana of its next spell. For instance, a troop that deals a basic of 2+Magic damage might deal 5 damage the first time for, say, 6 mana, then 6 damage for 7, 7 damage for 8, etc. Obviously, the more potent the spell, the higher the mana cost might be (like +3 mana per spell, for instance).
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Taunt: I admit, I stole this idea from another game!
Basically, a Taunt creature would have a ton of armour and/or life. Once the spell is activated, this creature would be the one all attacks are targeted towards. The spell might only last for a limited number of turns, and only silence can stop it. Ahah, you wanted to finish off my Druid? You’ll have to go through Tauntinator first! - Excessive: creature with excessive would have an amazing ability, with a rather huge downside - all other allied creatures would suffer because of it. Basically, the idea is that once an excessive creature is charged, they would cast an awesome spell, but all other allies would then a huge stat malus. For instance, you’ll get a creature called Excessive Destroyer (I didn’t say I thought the names through!). For only 8 mana, the Destroyer would deal 5 damage to all enemies. Sweet: cheap and massive AOE. In exchange for that, all your other allies lose 4 life. Or 1 magic. Or all are silenced. Excessive troops would be wonderful, but would have to be delicately handled in a line-up, from your end like from your opponent end. For you, it means knowing that you can only use it when the downside is acceptable, which might not last a lot. For your opponent, it means choosing between focusing it to avoid its massive spell, or letting it grow to see all your creatures suffer. I really like that idea. ^^
- Venom: also a classic in a lot of games. The idea is that this troop has a spell allowing it to kill off ANY damaged creature. Sounds OP? Well, obviously this troop would have ridiculously low stats and should be protected at all cost. At level 15, we’re talking a troop with 4 life, 3 armour and 3 attack.
- Death Cheater: a troop with Death cheater would simply… resurrect. Basically, the idea is that creature with this ability would have to be killed twice. They might not be the most amazing troop in terms of stats or spells, but having to kill them twice means you go to battle with 5 troops instead of 4.
- Life Giver: a counterpart to the Death Cheater, the Life Giver gains the ability to resurrect one of your fallen ally. The spell would cost a huge amount of mana; but could really turn a game around and might make for some pretty cool mind games if you resurrect a troop with Death Cheater. ^^
- Team Player: we already have troops that can increase the stats of your other creatures. What about one that reduce the cost of their spells? The Team Player ability would reduce the cost of all spells by 1 mana or more. That’s the spirit!
- Gravedigger: a grave-digging creature would get additional stats whenever a troop, ally or enemy, dies. That stat might be random or not. We could have the Grave Plunderer, who gets +3 to a random stat whenever a creature dies, or the Fallen Warrior, who gets +2 Attack whenever a creature dies, or the Ghastly Wraith, who gets +2 life…
- Spell Eater: pendant to the Grave Digger, a spell-eatingcreature would gain stats whenever a spell is cast. Awesome in your team, but get a huge target on its back on the opposite side…
- Mass modifier: just like troops with AOE (Webspinner / Behemoth, etc.), the mass modifier would affect all enemies; but rather than dealing damage or applying some mass debuffs, the mass modifier would decrease the stats of all enemy creature. For instance, the Shrieking Harpy could decrease the armour of all opponents by 5. So far, we only have Golem and a weapon that have this ability. Gloom Leaf also in a way, but he also benefits from it directly by stealing the stats. The mass modifier doesn’t steal anything, it just weakens everyone in its wake!
- Immunity: a creature with immunity cannot take damage from skulls and spells for a limited amount of time. The way I see it, rather than being a spell to use on oneself, immunity would be used on other units, much like a Priestess choose who she gives armour to. An immunity-giving creature could target the top creature, or the Tauntinator to make it more potent for 2/3/4 turns…
- Ticking Timebomb: the ticking timebomb, once activated, can work in two ways. Either they deal a small amount of damage to EVERYONE until it dies (a slow and horrific death) at EVERY turn. Or it just start a countdown and will explode in X turns, dealing massive damage to all enemies if no one managed to kill it sooner. This troop is a goner, but it goes with a bang!
- Supernova: at the start of each turn, the supernova gains +1 to all stats. It starts slow and can slowly build to be a force you can’t ignore. Coupled with an immunity-giving ally or some buffing spells/troops, the supernova has to be reckoned with. Do not laugh at its ridiculous starting stats. If not dealt with promptly, this creature will be the MVP of the battle.
- Retaliation: creatures with retaliation will always fight back. When you target them, they immediately counter attack. They might not have a high attack, but their huge life pool make them a real pain on the battlefield. A typical Retaliator would have stats such as 3 armour, 3 attack and 18 life. You can hardly burst it in one go, and they deal 3 damage to anyone targeting them. Just pray no one can buff their attack.
- Armoured: this concept is stolen from Solforge (which might be stolen from somewhere else, and I have no shame). Armoured creature are protected thusly: if a creature has 4 armour, that means they absorb 4 damage each time they are targeted. To deal them damage, you therefore need to apply at least 5 damage. And 5 damage only deal 1, since 4 are absorbed… Sounds gimmicky, but can prove really potent.
- Hinderer: the hinderer is super annoying, just in case the name wasn’t a give away. It makes all enemies’ spells costs a lot more. It might not do much more, but its ability can really be a nightmare. You thought your goblin was fast? Well now it needs 12 mana to activate. Not as fun, heh?
- Converter: maybe a bit gimmicky, but could be fun. Heavy RNG though. Target a creature to turn it into a random creature of the same rarity. Your Satyr is almost dead? See what you get in its place! That enemy Abhorat has ridiculously huge stats? Maybe converting him is a chance you want to take…
- Double Down: a creature with the double down characteristic might cast its spell twice. The spell might not be huge per se (for instance, at level 15, deal only 7 damage or give only 4 life), but the double effect might make it really big (14 damage or 8 life? yes please!).
- Tribe Leader: a tribe leader gains stats at the start of your game according to how many creature of the same type that it is are on the battlefield, ally or enemy. For instance, the Goblin Leader would get +1 to all stats for each goblin on the battlefield. If you have 3 allied goblins, it gets +3 to all stats. If your enemy has 2 goblins, it gets an additional +2 to all stats, increasing all its basic stats by 5.
- Slave Trader: just like for the Summoner ability, the slave trader can only be useful if you have an empty space on the board. Its ability (which is quite expensive), allow you to steal a enemy creature. According to the card rarity or the price of the spell, the slave trader could chose an enemy or steal it randomly, until the end of the match or for a limited number of turns. Sounds fun.
- Berserker: whenever a creature with Berserker takes damage, increase its attack.
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Simple-minded: these creatures have pretty good stats overall but one problem: they have a 75 % chance to target the wrong enemy.
- Nimble: a nimble creature has a 50% chance to dodge any type of damage. Not huge stats, but oh so annoying.
- Gift of Life: a creature with this ability has a positive effect on all allies on death (for instance, once destroyed, give +5 life to all allied creatures).
- Curse: on the opposite side, a cursed creature will have a negative effect on all enemies on death (for instance, all opponents lose 5 attack).
Also, I know we are starting to get quite a lot of summoners, but I like the idea of a troop that can summon any other random troop rather than a specific one. Sure, you’re probably getting a Fortress Gate or a Dwarven Miner, but what if that summoner gave you a Keeper of Souls or a Venoxia? It might be called the Sinister Summoner, and the RNG could add some fun moments.
I’m done now! But I’ll probably get some new ideas later! 
Edit: I accidentally press the send button but I wasn’t finished! 
Seems we share some of them - better chances to convince the devs 