There are two different ways to win:

1. HP Method

Reduce your opponent's HP to 0 using whatever strategy you choose (Hero's melee attack, spells, Hirelings' attacks, Hero's ability.). Upon knocking your opponent out you win the battle.

For example:

2. Portal Method

If your Hero (or your opponent's Hero) reaches the opposing Portal tile and can survive for one full turn, they will win the match.
  • Note: using a Hireling to occupy the opposing Portal tile will not win the battle. It must be a Hero.