This video shows you the final boss battle, after watching this video i managed to kill skullmageddon 1st try... NOTE - I used spin kick (level 4 only) instead of the dragon swarm...
Credit goes to Gamestestimony for the video.
Also on stage 10 there is a shop hidden away, its where there's 3 falling platforms that you have to jump across (you may notice an arrow in the background pointing down towards it) and if you stay on the last
falling platform you'll go down to the underneath level to where the shop is, i advise to buy lots of lives, 9 is the maximum you can have... Good luck!
Hope this helps