Here are some level codes (press 'HELP' on the title screen and type one in):
02-"AMEOBA" | 07-"FLIPME" | 11-"JAMMIN"
03-"BLOOOP" | 08-"GEEGEE" | 12-"KIKONG"
04-"CHEEKI" | 09-"HANDEL" | 13-"LAPDOG"
05-"DOINOK" | 10-"ICICLE" | 14-"MIKADO"
06-"ENIGMA"