Storyteller Jimmy - pretty good card as he has good attack and a good hp total. His aura also makes it so he is like a tank, being able to take more hits than someone else with his hp. Due to this he can be used to buy you some time. Can dish out some serious damage with Gunslinger Kyle buff.
Bandita Sally - great unit for 2 cost, she has good attack speed and great damage, can be used as a sneaky push whilst people are fighting and the enemy is low on energy. Or she can be used to shutdown headhunters like Dougie. She can also be used to pick of a unit on low health. Combos well with Gunslinger Kyle.
Calamity Heidi - great stats for only 2 cost. Great damage with Gunslinger Kyle.
Smuggler Ike - Same use as Sally, but you can also play him whilst you are pushing, but play him at the back side where the NK is, so that he goes into the enemy area with a buff. Combos well with Gunslinger Kyle.
Alien Clyde - Strong Fighter with a good HP total, in addition he applies a dot to an enemy unit that takes a lot of health by the time they are in fighting range.
Fireball - great spell that is used to deal a lot of damage to units clustered together, that often happens around Jimmy and Cartman. Can also be used to finish of a bar of NK health.
Rats - Can hard counter assassins and ranged units, whilst also being able to deal a lot of damage to fighters. Combined with Gunslinger Kyle, they can melt through fighters and do a LOT of damage to tanks. They can also be used as a sneak attack to the NK and can take a bar of health due to Kyle.
Sheriff Cartman - Decent tank, but his AoE ability is useful, but when paired with Gunslinger Kyle, can become deadly.
Nelly - Good attack with a good amount of health, in addition to an AoE attack. Due to this she can easily deal with rats and gnomes, but also clusters of enemies too. Also pairs really well with Gunslinger Kyle's buff.
Terrence Mephesto - A ranged attacker that has AoE damage. Whilst the damage may not be immense, the attack speed makes up for it. Is used primarily for dealing with rats/pigeons/gnomes, but can also be used to deal damage to multiple enemies due to his AoE attack. He also has flying which makes him harder to hit. Combos really well with Gunslinger Kyle.
Hookhand Clyde - Great attack power with decent HP, but his warcry is what makes him really good as he can one shot a lot of units. However, there is a chance that it hits the NK, so play him when there are 2 or more enemy units. Also don't play him when the only enemy is a tank.
Gunslinger Kyle - not bad attack and low HP means that he can be burned through with ease, but his buff can turn the tide of a battle. The buff synergies with most of the cards in the deck and can be used to clear the board or to claim a bar of HP when you need to.