Instructions
Play through the game until you reach Gnasty Gnorc at the end. A cut-scene will play, and then Gnasty and his band of thieves will begin to attack you.
Set flame to the rope connecting to the wooden platform behind Gnasty. This causes him to start running away, but you do not need to chase him just yet.
Attack all of the thieves with your flames. This lets you collect the gems without worrying about Gnasty harming you in the meantime.
Charge after Gnasty, never slowing down as you reach his platform. Immediately flame Gnasty when you reach him. If timed properly, you can attack him before he attacks you.
Run after Gnasty again. This time you must be quick about jumping to each platform, because they recede into the wall.
Roll away from Gnasty's laser when you catch up to him. Immediately flame him again to win the fight and beat the game.