Initiative determines the order in which some card interactions will happen. There are some occasions where the order of the cards' abilities can turn the tide of the battle.

All On Reveal, On Battle, and After Battle abilities are affected by Initiative.

Let's use Chaos and his ability as an example. In a given scenario in which both players play Chaos at the same time, the cards from the player with Initiative will be revealed first. 

That player's Chaos will trigger his ability first, moving the opponent's Chaos to the opponent's hand. 

Initiative is represented in the game by a race flag next to the player's name. This flag will determine the order in which the cards will attack each other. The initiative is assigned randomly to one of the two players first. After that, it switches between players every turn.