Twilight was deeply against this, but she doubted her consent had anything to do with it, Nightmare Moon would end up raping her one way or another. Nightmare Moon said "Now... I think we've had enough talking, so why don't you be a good little pony..." Nightmare Moon thrust her flaccid dick in front of Twilight's face "... and get this thing hard enough for the impending penetration hmm?" Twilight simply opened up her mouth, then as soon as a single inch was pushed into her mouth, she bit down as hard as she could, needless to say, Nightmare Moon was not a big fan of the pain Twilight was inflicting on her new genitalia.