This is by far the toughest of the underground "digging" challenges. It frustrated me quite a few times, too.

From the very start (middle of the screen)... Go down two blocks, all the way to the left to the wall, down to the plant, all the way over to the right (one block from the wall), down three blocks, back to the left, down to the water spout, up the water spout then left to the wall, down three then right to the 2nd water spout, up the water spout, right then straight down and you are there!

Always try to avoid hitting the spiked blocks yourself and try to keep Kaguya off them as well. Not only do they cost time but they knock her back and waste even more time. Don't waste time trying to bloom plants other than the one directly in your path. Never make a path that Kaguya cannot follow by either dropping off an edge, being blown over a spiked block or going up a water spout. Also, remember with regards to your jumps - You can double jump then dash to help you get to hard to reach areas!

Good luck! Let us know if this helped?!