Revealing mistake: In the beginning when the commissioner is talking to Batman in the batmobile, as the camera shakes, so does the image on the screen indicating a blue or green screened image. (00:03:15)
Continuity mistake: In the first shot that shows a high view of Mr. Freeze standing on the stairs, his ice gun is pointed up. But, when it shows him again, the gun is resting in his hands. The next shot shows him bringing the gun into his hands again. (00:03:50)
Revealing mistake: When Batman is doing his little sliding stunt on the dinosaur exhibit when he and Freeze meet at the beginning, it's obvious that he has roller skates on and is on a rail. (00:05:10)
Other mistake: This one is hard to describe. At the start of the movie, when Freeze and his gang are robbing the museum, Freeze looses his gun and it flies up to land on some sort of higher surface. However, it looks REALLY fake when it lands, perching right on the edge, which would be impossible for such a large weapon to do if thrown at that speed and from that angle. (00:05:25)
Continuity mistake: The first confrontation with Mr. Freeze and his henchman involves them skating around a large ice covered area. The henchman are not using ice skates, but rollerblades. In the same scene we see ice skating blades pop out of Batman and Robin's boots, but when we actually see them skating, they are on rollerblades as well. (00:06:45)
Revealing mistake: In the opening heist at the Gotham Museum of Art, just after we see the large diamond soaring through the air and Batman incapacitating a goon, Robin skates over to a statue to remove its spear to use it as a vaulting pole. When he whacks the spear to remove it from its position, the icicles on the statue wobble, just like fake rubber icicles. (00:08:20)
Other mistake: When Batman and Robin are falling after Freeze after they have jumped out of the rocket, Batman lands on Freeze and the diamond slips out of his grasp. However, you can plainly see that Arnold Schwarzenegger simply throws the diamond behind him. (00:11:55)
Revealing mistake: After Arnie freezes Robin, then freezes the doorway, then wipes his hand on the ice to wave goodbye to our hero, you can see that the clear spot is there before he wipes it with his hand. (00:13:50)
Revealing mistake: When Batman puts a frozen Robin in the water, you can easily tell it's a dummy/model of some sort. Obviously it's not Chris O'Donnell, but it hardly looks even remotely real. (00:14:00)
Continuity mistake: In Dr. Woodrue's lab, two thugs carry Antonio Diego over to an experiment table and chain him to it. The thug on Diego's left has a cowboy hat on. However, just as that thug is pulling Diego's mask over Diego's head a few shots later, the thug's cowboy hat is gone. This same thug also disappears from the aerial shots of the lab as Dr. Woodrue is exclaiming over his genius of turning Diego into Bane, a super soldier, with Venom. Later, when Bane breaks free of his restraints, the thug just shows up out of nowhere to try to hold Bane down. (00:16:00)
Other mistake: When Antonio Diego is being pumped up with Venom in Dr. Woodrue's lab, the tubes attached to the prisoner's head keep disappearing. It's in the shot where the camera pans from the foot of the exam table to Diego's (Bane's) right side. (00:16:50)
Continuity mistake: When Dr. Freeze bends down to kiss his wife right before his accident, there is a tube of some sort behind her (in the distance), then as he kisses her the tube is gone. (00:20:15)
Continuity mistake: When Pamela Isley is reborn as Poison Ivy, she is covered in vines. One vine runs across her chest. After she kisses (and kills) Dr. Woodrue, the vine across her chest is gone. (00:23:45)
Continuity mistake: In the car on the way to the observatory, Pamela Eisley puts on a perfectly straight-haired and slightly red/pink colored wig. But when she is at the observatory, her wig is brown, has numerous fly-aways and has long bits on the sides. (00:32:50 - 00:34:40)
Continuity mistake: When Dr. Pamela Isley and Bane first arrive in Gotham City and are driving to the Gotham Observatory in their (stolen) red car, Dr. Isley is putting on a wig. When she grabs the wig out of the box and puts it on her head, you can see that she has black gloves on, but the gloves are missing when she is looking in the mirror and says to Bane "Gotham Observatory, Bane. And step on it." (00:34:05)
Deliberate mistake: When Barbara Wilson/Batgirl first arrives she is standing on a ledge beside the front door when Robin answers the door. She then exclaims, "Oh. Uncle Alfred." However she could not possibly have seen him, not just because of her angle, but also the fact it is after that statement that he first comes into view. (00:34:10)
Factual error: Why is there a stellar observatory in the middle of a very large city, most of the stars would be drowned out by the city lights to the point of the observatory being useless. Also, the dome is very high up on top of a "building". Such buildings need to flex a little bit in the wind to keep them from breaking, this would make it impossible for the telescope to focus on anything for a timed exposure of film to make those neat pictures of galaxies and such. (00:35:20)
Continuity mistake: During the press conference, Julie's hand swaps from being lowered to brushing her hair between shots. (00:35:57)
Continuity mistake: At the observatory, when Bruce gives Dr. Isley's (Poison Ivy) proposal back. She grabs it with the printed part toward her, but in the next shot, she's holding the paper with the painted part facing away from her. (00:37:10)
Continuity mistake: Ivy extends the threefold invitation to the Botanical Garden event, but a shot later, it's folded and held against her chest. (00:38:00)
Chosen answer: Purely a creative decision, but based on the tone of this question I don't suppose you're honestly after an answer so much as you are just looking for someplace to express your distaste.
Phixius ★
Because Schumacher wanted to base the suits on Greek sculptures hence the nipples. Don't forget Robin's shorts or Batman wearing different colored cowls in the comics, perhaps this was a nod to that.
Rob245