There are 5 stages in total. For each stage you choose, the strength of the monsters you face will differ. The more difficult the stage, the more tickets you need to spend to participate.Regardless of which level you are on a particular stage, you are free to challenge other stages as well.
On levels
Levels represent the number of monster you will face on every stage. For every stage, there exists 16 levels in total. The higher the level, the more number of monsters you will have to face at once. You may not proceed to the next level of a stage until you have cleared the previous level.
Rewards
Rewards will be given out once you reach certain levels of a stage and are claimable from the Rewards page. Try your best to get as many as you can!