Out of all the many amazing costume ideas out there, perhaps the best thing about coordinating with your friends is that it's a guaranteed way to have the most fun Halloween ever. (Not to mention, the IG possibilities are endless.) And as it turns out, when it comes to group costume inspo, four is the magic number: From The Wizard of Oz to Sex and the City, look no further than these classic ideas for the best four-person Halloween costumes you'll see this year.