This is indeed Rainy, she has a nightmare version because her only two friends were super-alicorny-and-awesome, but she was a regular pegasus. She has a false horn that is keeping her in nightmare. If you snap it, she returns to normal. And she can use the dark aura in her mane/tail as a hand of sorts. It can attack you, but you can't hit it. #NightmareRainfeather #Rainfeather