Some quick tips: You can get x100 multiplier in an easier difficulty setting. This opens up the final ship which might help with completing Frantic mode. Once into Survival mode, take both +20% powerups from the shop (Kamikaze and Commander) as their drawbacks have no effect in Survival mode. Finally, remember enemies don't hurt you, only bullets do.
At first I was cursing the game for not having hotkeys, as it was difficult to cast meteors quickly enough to kill champion ninjas. But I just realised you can hold shift to quickly cast multiple meteors which makes a HUGE difference in getting the hard badge. Once fully skilled up you can cast 5 meteors in a row which kills a ninja outright. Please rate up this comment to keep this info visible.