All creatures and planeswalker have an initiative value. This value determines the unit's place in the turn order and how often it recieves turns. A figure with a higher intitiative value will move and act more often than one with a lower initative figure. In addition the the initative value on the unit's card each unit also recieves a random bonus to it's initative when summoned. This allows units of the same base initative to be higher or lower in the turn order based on the bonus score. The final value cannot be viewed by the player.
An Iron Grappler has an initiative of 5, while a Child of Night has an Initiative of 4. In the course of a game, the Iron Grappler should get 5 turns to every 4 turns the Child of Night recieves. However, each unit will reiceve a bonus to it's iniative that may change how many turns each gets.