(This entry is under construction)
About
The term “magical girl” is used to describe female characters in various media with the ability to take on an alternative form in an often decorative and visually stunning way. 
History
While the idea of transforming into a different being goes back to ancient times [2],Akko-chan of Himitsu no Akko-chan is typically accepted as the earliest magical girl after being published in the shojo manga magazine Ribon in 1962. Himitsu no Akko-chan would would go on to plant the seed for later magical girl themed media [1].
In 1992, however, Sailor Moon revolutionized the magical girl genre by introducing the first crime-fighting magical girl and popularizing the idea of a magical girl team. Due to its success, many magical girl series after Sailor Moon incorporated similar concepts [3]. It can be said that while Himitsu no Akko-chan introduced the idea of a transforming female protagonist, Sailor Moon molded the genre into what it is today.
Reception
(Yeah, I really don’t know)
Generally magical girls have been positively received particularly by fans of anime.
Some feminists believe magical girls to be a good example of “girl power” as the girls typically serve as strong heroines who don’t continually rely on male assistance. Others argue things such as typical magical girl attire and its take on beauty are a bad influence for young girls who are the main demographic for the genre [3].
Impact
A new genre of anime was created as a result of the success and appeal of early magical girls.
Fandom
Magical girls have a considerable following and their presence is widely felt in many online communities, especially those concerning anime. Often the most notable and discussed part of of this genre are the transformation sequences.
Related Memes
Fanime Transformations
Because of the popularity of transformation sequences, many fans of the genre like to create their own transformations. Many times these transformations are used in fan-made anime with a magical girl premise. The skill of these videos can range greatly.
While They Transform
(May not be a meme) “What do villains do when they transform?” and variants of this question are often put as a response to lengthy transformation sequences. This concept is also used as the subject of parodies and fourth-wall jokes. 
Search Interest
External References
(Please help me find more reliable sources)
[1]Wikipedia – Magical Girl / Posted on 3-14-2003
[2]Wikipedia – Shapeshifting / Posted on 6-11-2003
[3]Wikipedia – Sailor Moon / Posted on 9-8-2001
[4]Television Tropes & Idioms – Magical Girl / Posted on ???