In each chain, winning a stage in Campaign opens the next one: stage 15 opens stage 22; stage 16 opens stage 17; stage 18 opens stage 19; stage 20 opens stage 21; stage 23 opens stage 24, which opens stage 25, which opens stage 26. The Campaign waves of all 26 stages add up to 404. Every stage is also played as a Heroic Challenge and an Iron Challenge.
