I’m guessing it’s probably either ninjas or assassins which are getting you. I usually leave level 9 until I’ve at least gotten through all of the rest of the levels – then go back to it. You’ll have way more firepower then. Only use your meteors if you absolutely have to, as you’ll need as many of those as possible to take out the boss ninja or assassin.
With assassins, I have found that crypts tend to be the best weapon.
For ninjas you’ll need something to set them off AS SOON AS THEY COME OUT (I prefer temples), and then some heavy firepower at the other end by your gems to take them out when they become visible again.
If you have trouble with boss ninjas in the later levels (particularly 14), you need to have two things:
1. Heavy, heavy firepower at the beginning
2. At least one Den at each entry point (maxed out with skills) – the poison skill, if you hit the boss ninja with it will keep on affecting the ninja while it’s invisible which will give you enough damage points to do the rest with your meteors.