Your mouse heroes also have a personality of their own and they can synergize better with other like-minded heroes. Their personality is defined by traits that are part of your NFT. Some Mouse Heroes have traits that tells us a little bit more about their temperament.
Your squad is determined by joining 3 Mouse Heroes, but synergy buffs will be applied as long as 2 heroes have matching traits. You can also match several different traits within the team, as long as 2 of the heroes share the same trait. By pairing mouse heroes with the same traits they gain synergy that gives them a buff to their base farm rate and will make them farm more efficiently as a team.
This increase in farming can be stacked so make sure that your squad of 3 contains as many mouse heroes with the same traits as possible.
It's important to note that Mouse Heroes of higher rarities with the same outfit do not like each other. This means that on the Lock and Load mode, Legendary and/or Epic Mouse Heroes with the same outfit will not have synergy bonus. On the other hand, Commons and Rares are fine with any outfit, they can have synergy even if they are exactly the same.