You could do all this... and i did!!! so i know how hard some of these are..
BUT there is a much much much easier way.
Basically go into your solo game and make your way to the throne room, go to the magic mirror and select Thorns Airship. Your aim in this level is to purely get over 3 million and finish the level.
If you have beaten this level and got the 'a' ranking achievement this should be easy... If you need a guide to refresh your memory go to this site
http://www.dmbledore.com/Kameo/ARanking/6AirshipA.htm this also has a video to help beat Thorn at the end, although to be honest eye of strength and themites bomb attack = easy win.
Once you do this you will unlock both the invincibility cheat and the ''one hit kill cheat''. Put these on and cruise to victory in all the levels. With this on most of the levels take about 10 minutes. Having this on disables score for the level BUT ACTIVATING THE CHEATS DOES NOT BLOCK GETTING THE ACHIEVEMENTS!!!
A few things to note- firstly the cheat will only be unlocked on that save file. Secondly on snow temple make sure you remove the one hit kill cheat as the walrus counts as a one hit kill for your enemies!!!
Really hope this helps someone as it helped me finally beat thorns airship, to anyone who has got that without this cheat i salute you as that level - particularly the thorn boss battle must be controller destroyingly impossible!