I would say 4 is pretty annoying granted you can farm there unlike world 5 which just plain sucks
World 1-3 is kind of a pain until you open up the shortcut. Then you can dash for the boss fight if you use clever methods and lure the army away XD
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XBL GT: Demon Ninja X2
"There comes a time in every man's or woman's life where they have to make **** up to cover their ass." - Hazama