Perfected Dreaming Leaf on Hard.
This song lags as well. Fortunately, the song is straightforward and it’s rather fun, so it took me just several tries.
Again, I tried to finish my attempt even if the combo broke, but the random-chance item still wouldn’t unlock. Then I found out I actually have two, not just one, items left to unlock. One is a room accessory called Mega Drive, and the other is a wall accessory called Original Poster 15. Wonderful..