Also, he is Jin. It's a complete Playing Against Type, as while Natsu is a friendly, loud, innocent and chast bare-handed Fire-user, Jin is an aloof, quiet, tsundere sword-user Ice-user. He also voices Hakumen, Jin's alternate self, but Hakumen's voice is distorted.
Mashima mentioned in Volume 10 that he once thought of Erza's entire adult life being All Just a Dream of young Erza, but decided against it when he realized what that would mean for the entire rest of the series.
Considering the problems she has as an adult (not the least of which is that the love interest she relied on so much as a child is Brainwashed and Crazy), this would have some serious implications for her mental state if it were true.
Her friends also were supposed to be the Quirky Miniboss Squad of the arc, rather than have a Bait and Switch with Trinity Raven. When he was writing their backstories Mashima decided that he liked them too much to make them serious villains.
Similarly, Erza's original character design had her as more of a Nubile Savage than the Magic Knight we know her as. Mashima's idea for her character was simply "a woman badass enough to scare Natsu" and everything evolved from there.
Makarov was supposed to die during the Tenrou Island arc.
Word of Dante: Everyone treats it as a well known fact that Lucy's mother died on July 7th X777. If you actually look through the series you might notice that while she did die that year, there's no mention whatsoever of the exact day or even month she passed away.
You Make Me Sic: Post something along the lines of "Who's your favorite Fairy Tail character?" online and take a shot every time someone tells you the genre is actually spelled Fairy Tale.
Or on the flip side, look up Fairy Tail stuff and see how many images of/links to fairy tales you get.