Board Thread:Game Discussion/@comment-4199297-20130630200721/@comment-2067839-20130701024150

Each of the reward-level bosses has the stats of something several levels higher. (That's why I use the term "pseudolevel" on my calculations and graphs.)  Level 15 is actually about level 18-and-a-half. If you manage to kill it, you'll find that level 16 is much easier.

Level 21 is the same as level 24; level 28 is the same as level 31; level 35 is 39, level 43 is 47, level 51 is 55, and level 60 is roughly what level 67 would be if the increases didn't stop at 60.