| rowspan="6" style="text-align:center;"|'''In order to play these maps on hard, you must complete the previous map on either normal or hard.'''<br/> ''(e.g., to do E-4 on hard, you must complete E-3 on normal or hard.)''
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| rowspan="6" style="text-align:center;"|'''In order to play these maps on hard, you must complete the previous map* on either normal or hard.'''<br/> ''(e.g., to do E-4 on hard, you must complete E-3 on normal or hard.)''<br>''Note: Clearing E-4 unlocks E-5 and E-6 at the same time, and '''both E-5 and E-6 consider E-4 as previous map.''''' That is, clearing E-4 on easy prevents you from attempting E-6 on hard regardless of what difficult you attempt E-5 on (if you attempt E-5 at all).