Though the first two crazed stages were possible with a lv20 bahamut cat, further progress needs higher levels. To unlock level 30 upgrades for special units, you need to reach 1600 user rank (you increase user rank by upgrading any unit). More Tips, Tricks and Tutorials: https://goo.gl/5v4WX9
Battle Cats Beginners Guide How to Beat XP Stages + Why 1600 User Rank is Important (S5E2)