Deltarune Chapter 5 has a few boss duos that you face, mostly in the final section when you're in Flower Castle. Yellow and Blue are the pairing that you fight before you head to the top of Flower Castle, and their fight takes place on the left side of the castle. So, you usually complete the right side where the caf is for the sake of having a shop, then move to the left side in order to clear the hedges in front of the large door.
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