We'll explain how each Trait works in Clash Royale's Merge Tactics mode, and explain the bonuses you can get from using them.

Combining Troops to build bigger and more powerful units can help you assemble a strong squad for Merge Tactics. However, it's not only just making a big squad, but it's also about stacking your team with the right Traits.
What are Traits in Clash Royale? These are characteristics each Troop has that, when stacked with other Troops of the same Trait, can provide your team with bonus perks, such as additional HP or bonus damage. Each Troop has two Traits.
All Traits in Clash Royale's Merge Tactics
There are currently 11 Traits in Merge Tactics. Each offers various perks and bonuses.
Ace

At the start of combat, the highest Merge Level Troop is assigned 'Captain.' Your team gains an additional 20% hit speed (for 4 seconds) whenever the Captain defeats an enemy Troop.
The bonuses for stacking the Ace Trait are:
- 2 Troops: Captain gains 30% bonus damage
- 4 Troops: Captain gains 60% bonus damage and gains 30% HP for damage dealt
Assassin

At the start of combat, Assassins will jump towards the enemy's backline Troops.
The bonus for stacking the Assassin Trait is:
- 3 Troops: Additional 35% Critical Chance and Critical Damage.
Avenger

Avengers gain bonus damage with each additional stack of a Troop with the same Trait. The last Troop standing will deal double damage.
The bonus for stacking the Avenger Trait is:
- 3 Troops: Additional 30% damage
Brawler

Brawlers will gain additional max HP the more you stack Troops with the same Trait.
The bonuses for stacking the Brawler Trait are:
- 2 Troops: Additional 30% max HP
- 4 Troops: Additional 60% HP for Brawlers; additional 30% for the rest of the team
Clan

Clan Troops will rapidly heal and gain bonus hit speed at 50% HP once per round.
The bonuses for stacking the Clan Trait are:
- 2 Troops: Additional 30% of max HP and hit speed
- 4 Troops: Additional 60% of max HP and hit speed for Clan Troops; additional 30% for the rest of the team
Goblin

A random Goblin will spawn for free next round when you have a Goblin Troop.
The bonuses for stacking the Goblin Trait are:
- 2 Troops: Gain a 2-Elixir Goblin
- 4 Troops: 60% chance of gaining a 3- or 4-Elixir Goblin
Juggernaut

At the start of combat, the Troops behind Juggernauts will gain an 8-second-long Shield.
The bonuses for stacking the Juggernaut Trait are:
- 2 Troops: Additional 30% Shield for Juggernauts; additional 15% Shield for the rest of the team
- 4 Troops: Additional 60% Shield for Juggernauts; additional 30% Shield for the rest of the team
Noble

Troops at the front of the team will take less damage, and backline Troops gain bonus damage.
The bonuses for stacking the Noble Trait are:
- 2 Troops: 20% less damage for frontline Troops; 20% bonus damage for backline Troops
- 4 Troops: 40% less damage for frontline Troops; 40% bonus damage for backline Troops
Ranger

Rangers will gain additional hit speed per attack when you stack Troops of the same Trait.
The bonus for stacking the Ranger Trait is:
- 3 Troops: Additional 15% hit speed per attack
Thrower

Throwers will gain +1 attack range and deal more damage to distant enemies.
The bonus for stacking the Thrower Trait is:
- 3 Troops: Additional 10% damage
Undead

At the start of combat, the enemy with the highest HP is cursed. Your Undead Troops gain 20% additional damage when that enemy is defeated.
The bonuses for stacking the Undead Trait are:
- 2 Troops: Curses 1 enemy; max HP is reduced by 25%
- 4 Troops: Curses 2 enemies; max HP is reduced by 50%
All in all, Traits can have a massive impact on your team's synergy and, ultimately, how potent your team can be.