Levelcodes:

 Level 2 : SZWS
 Level 3 : ZS2S
 Level 4 : ZZPS
 Level 5 : SW3S
 Level 6 : SXES
 Level 7 : ZW4S
 Level 8 : ZX9S
 Level 10: WZFS
 Level 11: XSJS
 Level 12: XZKS
 Level 13: WWMS
 Level 14: XWAS
 Level 15: XMAS
 Level 16: XX0S
 Level 17: S25Z
 Level 18: STWZ
 Level 19: Z22Z
 Level 20: SP32

By Kevin J. & Sebi D.