War Pass is a seasonal event, during which you will receive rewards based on the amount of pigs you have collected. Remember that the War Pass Season lasts for 2 months, followed by a short break as soon as it ends. You can access the War Pass from the destroyed Shockwave Spire or the level menu in the upper left corner of the game screen.
When the War Pass Season starts, you will be asked to choose your team for the season. Teams provide different boosts to your characters, so pick well! Once a team is chosen, it cannot be changed during the season. After each day, the landing team receives more pigs as rewards to help you level up the War Pass further.
There are two options in War Pass: the free War Pass, which provides rewards for every three levels, and the purchasable Prime Pass, which offers new rewards on every level. Remember that you will unlock a bunch of Rare, Epic, and Legendary accessories and exclusive characters with a prime pass. You still need to play and collect the pigs to receive all the rewards. Best rewards are provided as you reach level 50!