Based on the title you may or may not decide to read this post. From so far of what I have seen of this site you probably will.
I realized many people on this site either don't take magick seriously, or they are making wishful dreams and not realizing that magick cannot do everything.
So here is my take on this subject:
Mermaids: Fact or Fiction?
What is a mermaid?
Mermaids are creatures which contain an upper human half and a lower fish half. They are different from mermen as both of them are of different genders (at least the upper halves are).
These creatures are well known throughout legends both new and old. They were referenced in the sirens that Odysseus faced in the Odyssey. In more recent times sailors who were made mad from lack of food and water (and women) looked at manatees and thought them to be beautiful mermaids and then you have movies like The Little Mermaid by Disney.
The idea of what a mermaid looks like has changed over the years as the tastes and styles have changed. At one point in the past mermaids were quite fat, whereas now they are quite thin. But either way the fish tail and human torso remains the same.
Mermaids have been both kind and caring, and vicious and ferocious. It just depends on what myth, legend, or story you are looking at.
A mermaid is a untamed entity that is close to his/her intuition and feelings and as such has different perceptions of the world then the rest. A mermaid opens their heart and lives with their feelings in tune with themselves. They represent wild freedom, rebellious spirits, and ferocious independence.
Mermaids are free creatures, ones that are untamable, and in the attempt to tame them you may end up hurting yourself. They are freedom loving and true to themselves and their emotions always. They follow their hearts and do right by them, and in doing so they gain more freedom than many people.
Mermaids exist on the astral plane. They are creatures which have either come from the minds and imaginations of Millennium of humans that have grown and evolved along the way, or they are creatures which exist outside of ourselves (depending on your belief).
Either way, yes, they do exist in some form or another. And yes, you can become one on the astral plane. You can become anything you can possibly think of on the astral plane if you try to. Yes, some forms will be more comfortable to you, and yes, some forms will be easier mobility for you, but you still can go as far as the imagination allows (and possibly passed that).
Mermaids do not exist physically (unless you mean manatees). I don't care who you are, what spell you do, what potions you drink, etc etc etc, you won't become a mermaid physically.
It is simply impossible.
Yes, you can go to the store and buy a tail and run around pretending to be a mermaid, but you will never truly become one physically. It is simply impossible to change your physical form to that extent (at least currently it is). And even if you could change your form to that extent it would be extremely complex and extremely painful as you are changing the structure of your very being.
I hope that this has cleared a few things up. ^_^