Image imported from derpibooru 
Original Description:
 

 
 
Fluttershy: My dear Rainbow… you lack… vision. You want to turn people into mermaids out of leg envy and for the loss of your career as an athlete, as a runner. You are so short-sighted about this, my dear blue girlfriend.
 
Rainbow: Fluttershy… what has gotten into you?
 
Fluttershy: mmmmm….. determination… bravery…. and perhaps a bit of righteous cruelty. That’s what has gotten into me. You see, my blue morsel… Mankind has been destroying nature for so long… and I will make them pay. I will sink their world, ship by ship, turn them into merpeople and make them clean up MY ocean, up to the last piece of plastic and trash.
 
Rainbow: Whoa, whoa girl, I am all in for ecology and nature, but you sound… totally like a villain. That’s not cool at all!!!
 
Fluttershy: It was your stubbornness that made me use the ATTITUDINATOR to become brave enough stop you. You’re fighting so you can watch everyone around you become a mermaid and now regret it when you find somebody of your same species that not only puts you in your place, but will own you too. Think Rainbow, Think!
 

 
Part of a series of drawings for :iconannonmyous:, whose SFW versions will be uploaded here some time after being in my Patreon (this one has been up there since October)
 
 
This is a standalone, (as you guessed and as you know) part of the Equestria Girls series of My Little Pony, following my fan-story Equestria Mermaids.
 
:iconannonmyous: wanted to see how the girls would turn out if they became their evil selves from IDW’s “Ponies of Dark Water” comic series
 
I thank you! Thank you! Thank you!