Hey UwUAmber, Kingaroo and xLunaa_!
I am here to give you my review of the map! Please remember that I am not a map judge and my opinion doesn't have effect on whether the map gets accepted or not, I'm just trying to give helpful advice! :)
Firstly the theme of your map is OKAY since while there is a map related about a mermaid (Ariel) this map has a slightly different concept and has a much better and more lively build!
Secondly the build of your map is GOOD the mermaid looks accurate to what a real mermaid looks like and there's plenty of other details to be seen as well!
Thirdly the parkour of your map is OKAY. I found it fun while playing it, it's varied and most of the parkour isn't floating which is good! However I think the map is TOO HARD for the Medium difficulty. I would recommend nerfing it by making the jumps easier or by adding more checkpoints, or by doing both! The map length however is great for a Medium map!
Good luck! :D