Child of Eden

This is are excellent guide for this level, for the Gold Star (100% + 800k) rank you definitely need some practice, but you can get the 800k in the few tries. Just follow the video, this is very detailed and useful guide.

This level is the hardest, in my opinion. Be ready for the multiple tries.

Also, you should know how to make octa-locks (perfect 8x hit in the rhythm of music), without octalocks you do not succeed.
And, you should get and save 3 euphoria at the end of the level - this gives you 100k. Without this bonus get this achievement will be much harder.
Again, just follow the video and don't forget about gathering and saving euphoria and, of course, octalocks.

All credits goes to SajikoSakura