Every Hero and enemy is one of the five Elements in the game. The elements are Nature, Fire, Water, Dark and Light. They are easily distinguished by the color of their attire or the color of their portraits. Element types not only play an essential part in synergy and elemental passive benefits like Willow's or Ignus' , it also provides advantages and disadvantages over other elements.
When starting a fight in the dungeon, you will notice that arrows are either red or green. Red arrows indicate that your hero will deal 25% less damage to that specific enemy. Green arrows indicate that you will deal damage without any modification with elemental types.
You will also notice that some enemies will have double green arrows over them. This means that your Hero has an elemental advantage over them and will deal bonus damage. The following have elemental advantages over the second: Nature beats Water, Water beats Fire, and Fire beats Nature. Dark and Light deal additional damage to each other. They will deal an additional 30% damage.
It is important to note that you can not land critical hits (CRIT) on an enemy with an elemental disadvantage. This means Fire can't CRIT Water, Nature can't CRIT Fire, and Water can't CRIT Nature. But Dark and Light can land crits on each other.
Bonus and penalty in battle
The following table gives an overview about the bonus and penalty given when one element fights another. The rows represent the elemental type of damage and the Defending columns represent the hero or the enemy that will recieve the damage. For example, a Fire source dealing damage to another Fire Hero will not gain any benefit and will deal 0% additional damage, wheras the same Fire source dealing it to Nature will deal an additional 30%.
Every element has a increased resistance (30%) to the element specific negative status effect (debuff) and an increased resistance (15%) to the opposing element specific debuff, in addition every Hero has a 3% Spirit resistance. Each star ★ that a Hero gains increases the resistance a little bit (about 0.5%, primary element resistance for each star is: ★ = 30%, 2★ and 3★ = 31%, 4★ and 5★ = 32%, 6★ = 33%).
So Fire Heroes resist better Fire. They take less Fire damage and have a better chance to avoid being Burned. They also have some poison resistance because Nature is the opposing element.
Light Heroes resist better Lighting and being Shocked but have no increased Disease resistance.
The following table shows the resistances for each Element.