Formations

Before any fight, you are able to select up to 7 heroes and place them into a 2 row formation. The front row consisting of 3 heroes, and the back row consisting of 4 heroes. You are also able to save up to 10 formations, to make it easier to select particular formations quickly.

Formations benefit from having multiple heroes of multiple races and classes, as if you have at least 2 heroes of a particular class or race (except for demons), you will gain an additional bonus either impacting your entire team, the enemy, or all other heroes of the same class or race. As you get more of a particular class or race (with the exception of demons), this bonus will either increase, or alter itself in someway, making the bonus even stronger.

Strategy
As a general guide, the front-line of your formation should consist of heroes that will be able to take more damage and last longer in battle to prevent damage reaching your back-line. So examples of good front-line heroes would be Zak, Kha, Leoric and ClockCrank. This is because your back-line should generally consist of damage dealers and utility heroes. Some examples of utility heroes would be Jeatah's mass healing, Victor's mass silence, Nekrosius' mass invulnerability or Medusa's mass stun and slow.