Any other variation may cause Hangyodon not to acknowledge that you've done it. The Scale Mermaid Armor is found to the southeast of the where the tiara was found. Here, you'll see cobblestone ...

Once you are there, you will find the Teal Scale Mermaid Armour ready to be picked. Go near the armor and tap on the hand icon to collect it. Once you do that, it will move to your backpack.