As Val Kilmer was getting out of his crow cage between takes, the chain snapped and the cage came down on his foot. His resulting limp is evident during the scene in which Madmartigan and Willow arrive opposite Fin Raziel's island.
The earlier drafts of the screenplay contained more background information on the characters Madmartigan and Sorsha. Madmartigan was originally a knight of the kingdom of Galladorn (the kingdom that General Kael mentions having destroyed to Queen Bavmorda) and that the character Airk was the only real friend he had, but Madmartigan's recklessness got him into trouble, as did his love affair with an Eastern beauty that tainted the family name. Madmartigan had a chance to regain his honor in battle, but he ruined the chance by deserting; this explained some of the bitter antagonism between Madmartigan and Airk. Sorsha was originally the daughter of the king of Tir Asleen, who was a good man (he is in fact the regal old man seen at the end after the fall of Bavmorda and Tir Asleen is restored, and can be briefly seen in stone), which suggested that Sorsha had the capability to be good; during the battle at Tir Asleen between Bavmorda's troops, Madmartigan, and the monster, Sorsha encountered her father and he struggled through the stone to ask her for help, which prompted Sorsha to switch alliances from her evil mother to the good side. All of this was lost in the final film but does appear in the novelization as well as the comic book mini-series by Marvel.
Willow originally said, "Goodbye, Elora Danan" when handing her over to Madmartigan. During editing, it was realized Willow wouldn't have known her name yet, and so it was redubbed, "Goodbye, little one."
David Steinberg, the actor playing Meegosh, slammed into the side of an ice rink while ice-skating during production and cut his eyebrow open. The stitches were concealed with makeup for the scene where Meegosh makes his departure for home.
During the close-up shots of the scene where Madmartigan and the soldier are being dragged behind the wagon, Val Kilmer was kneeling on a pedestal behind the wagon, while his stunt double was dragged behind letting the stunt man's legs take the beating.
A 13lb animatronics baby capable of moving its head and opening its mouth was used for the action scenes. This baby weighed more then the actual baby. And a more flexible prop baby was used in scenes where Willow falls with it.
According to the press kits and subsequent novels, the two-headed dragon was named "Eborsisk", a reference to the movie critics Gene Siskel and Roger Ebert. The word does not occur in the film but made it into some reviews.
The box office receipts were less than expected, so writer George Lucas continued Willow's story in books rather than in movie sequels. The three books are collectively known as "The Chronicles of the Shadow War" and share a writers credit for Chris Claremont and Lucas. They are: "Shadow Moon" (1995), "Shadow Dawn" (1996) and "Shadow Star" (2000)
WILHELM SCREAM: It is heard three times: 1, during the chase scene after the escape from the tavern as the soldier's chariot crashes and he is sent flying, 2, At Tir Asleen, when the Brownies trigger the large spear shooter that hits several soldiers, and 3, In front of Nockmaar Castle as a horseman is cut down by the Army of Galladoorn, three seconds after the Brownies emerge from under a helmet.
Word from Ron Howard is that part of the two-headed dragon "Eborsisk" was modeled after Clint Howard, his brother. He stated that since Clint has had many cameo appearances in his films, and Ron couldn't find a part for him in this one, he modeled the dragon after him.