Executive Meddling: The studio wanted a PG-13 Alien Vs Predator film (the "unrated" DVD version ended up being basically the same movie save for several seconds of minor gore restored). This decision was later blamed on notorious Fox executive Tom Rothman. He was also alleged to have demanded present-day Earth be the setting instead of out in space in the future.
Scully Box: As revealed in the Special Effects commentary tracks for Requiem's special edition, this was used to make the 6'2 Tom Woodruff Jr.'s Predalien tower over the 7'1 Ian Whyte's Predator.
Troubled Production: Most of the trouble was in actually getting the project to the point where they could film anything. The initial draft was written by Peter Briggs in 1991 and set to go into production once Alien³ had been released, but the rights holders for the two franchises spent the next few years battling out over the direction of the screenplay, resulting in several screenwriters coming and going and various new drafts being produced, but nothing of any real substance being accomplished. Eventually the project slipped into the background, and wasn't revived until 2002, when Paul W.S. Anderson approached the studio about producing the film. Anderson eventually got a workable screenplay by ditching everything bar a few story elements from the original Briggs draft and writing his own story from scratch. As with Resurrection, filming was pretty trouble-free, but the studio were convinced that an R-rated film would not be a box-office success and ordered Anderson to make the film PG-13 at most. There was also a spat over the writing credits, which the studio had recommended should go to Briggs and Anderson for the story, and Anderson and Shane Salerno for the screenplay, only for the Writer's Guild to inexplicably deny any form of credit to Briggs or Salerno and instead award co-story credit to Alien writers Dan O'Bannon and Ronald Shusett, who had never been anywhere near the project. The end product was a box-office success, though ironically made less money than the previous year's R-rated Freddyvs Jason.
A very early script of the first film would have had the film take place in the same timespace as the Alien trilogy, complete with a Ripley expy!
Jerry Goldsmith and Alan Silvestri were planning to team up for the first film's score but Goldsmith's battle with cancer (and eventual passing) prevented the pairing from occurring. Which would have gone against his belief that there's no need for two composers working in the same film. He only needed an additional composer if he was pressed for time (as with Star Trek: The Motion Picture and Air Force One), and he couldn't make the deadline. "How many composers does it take to screw a light bulb?", indeed.
As mentioned on the main page, the Brothers Strause mention on the commentary that they had an idea of the ending where after handing off the Predator weapon to the military, the "rescuers" lifted up their weapons and the screen would cut to black with the sound of the rifles firing full-auto. Ouch.
Similarly, on the commentary, they mention that Colonel Stevens was originally supposed to be Garber from Predator 2, but talks with Adam Baldwin fell through.
Some of the script drafts toyed with the idea of Alexa getting on the ship and leaving with the Predators for the stars, which is the ending we all secretly wish they'd gone with.
Toilet Humour: Believe it or not, Aliens vs Predator was dreamed up when one of the creators, who was struggling to come up with ideas for a new comic book series, decided to take a bathroom break. During his break he realized that Fox owns both Alien and Predator franchises. He came running back to the room with all of his colleagues shouting "ALIEN VERSUS PREDATOR!" Yes, that's right; AvP is the result of a really good poop.note We can only assume Requiem was the end result of a really bad poop. *rim shot*