YMMV / Bangai-O

• Breather Boss: Bangai-O has scads of these, usually consisting of green orbs... whose only mode of defense is regenerating health. Of course, they do tend to be found at the end of rather difficult levels.
• Demonic Spiders: The higher-tier bots in Spirits. FastBots roll around in their impenetrable armor at you to damage you, then open up to hit you. NinjaBots fly around at high speed, blocking your shots with their sword, which they also use to cut you up. BigBots fly around slowly, but can reflect your shots back at you, and swipe you for massive damage. And finally, there's Longai-O, who can use EX attacks just like Bangai-O can but without any pretense of a limit to it. Some of these are, thankfully, cakewalk in Missile Fury, especially when you have access to both dash AND freeze.
• Moe: Mami. This is emphasized in the game over screen shown when you refuse to continue.
• Nintendo Hard:
  • The tutorial for Spirits concludes by telling you how to turn on the invincibility cheat. That should give you an idea of what you're going up against. And the last mission is pretty damn hard.
  • Missile Fury ramps it up: You can die in seconds on the very first stage if you don't know what you're doing.
• Scrappy Mechanic: In order to give custom levels to other people, Spirits will turn the level into a sound clip, which is then played through the speakers. In theory, this eliminates the pain of using the now-defunct Nintendo WFC service to exchange levels; just record the sound, save it into a sound file—preferably a lossless format like .WAV or .FLAC—and share it with your friends or post it on the Internet. In practice, a lot of people have trouble getting the DS to recognize the sound clips unless their set-up is absolutely perfect.

---