Revealing mistake: When Dino (Mirage) throws Hatchet over to the other side of the freeway, Hatchet doesn't even make the security van right next to the car he crashes move, while he should have. His arm is basically going right through the van.
Continuity mistake: The shot of the Apollo 11 capsule approaching the moon is missing the lunar module, which is then seen attached to the craft in the next shot.
Revealing mistake: In the highway chase scene, when Crowbar knocks down some signs for the other two Dreads to use them as ramps, the simple structure supporting the signs changes to a far more elaborated one when the Decepticons launch from it. The signs are even replaced with actual platforms, much longer, wider, and with different angle and separation than in the previous shot.
Continuity mistake: Towards the end of the movie with Chicago in ruins, the river alternates from green to brown through the entire battle.
Continuity mistake: When the guy in the back seat gets out of Epps' car, he is wearing a baseball cap and a Motley Crüe t-shirt. In the next shot, he is wearing full tactical gear - instantly. (01:37:15)
Continuity mistake: In the scene where Sam meets Dylan for the first time, the distance between Sam and Carly keeps changing.
Continuity mistake: *Spoiler* After Cybertron is pulled into Earth's orbit, they show that it can be seen from the earth's surface, pretty much the entire sky is taken up with Cybertron. However, in several scenes afterwards the sky is shown in the background as being crystal clear again.
Continuity mistake: In the scene where Sam, Carly and others slide down the collapsing building, the shot from above reveals only one window hole where they could have jumped from, and Sam and Carly are sliding quite far off to the side from the hole.
Continuity mistake: In the highway chase scene, one of the Decepticons knocks down the freeway sign which causes the signs, originally facing the on coming cars, to flip away from them. The other two Decpticons then use the signs to as a ramp to get further down the road. This should be impossible because the signs didn't land that way. When the Decepticons land, the signs are pointing the first way again.
Revealing mistake: Right after Sentinel finishes his speech at the tower, there is a shot where a lot of ships are shooting at buildings, but when they smoke from the explosions is gone, none of them is damaged. This mistake can also be seen when the dropped US soldiers are being chased and shot at by Decepticon ships.
Continuity mistake: Towards the end of the movie, when Dylan is pointing a gun at Sam, he has both hands on the gun. In shots of Sam, one of his hands is on his side.
Factual error: Neil Armstrong's first step onto the moon as depicted in this film is incorrect. In real life he descended the LM ladder until he was standing on top of the little dish at the end of the landing leg. He then jumped back onto the ladder (the lower rung of which was a few feet up) to see if he could climb back up. He then jumped back down to the LM footpad. Then he stepped off into the dust to create the first footprint on the moon. The film shows him climbing down to the lower rung of the ladder, then just jumping into the dust where the initial footprint is immediately trampled by his movements.
Factual error: Big Joe has an AT-4 rocket launcher, which gets loaded before he wants to shoot the pillar. AT-4's are not reloadable.
Continuity mistake: Towards the end of the film Carly is holding Sam, in some shots she has dirty hands in front of his shoulders and in other shots she has clean hands that are over his shoulder.
Visible crew/equipment: During Sam's first meeting with Bruce, at one point, there is a reflection in the ornament on the left side of the desk that shows a large black mass moving in the same direction as the shot is moving.
Revealing mistake: Toward the end, when Sam is going to destroy the tower he gets kicked in the stomach by Dylan. When Sam falls he lands on another part of the destroyed building, you see the chunk of building that he lands on conforms to his body, showing that it is made of foam to soften his landing.
Revealing mistake: When Megatron blasts the Lincoln statue and sits in his throne there is a CG mistake. His left foot is embedded in the stonework with one of the wheels (only 3/4 is visible).
Continuity mistake: In the NASA radio room, There are two men standing beside a cabinet. One a white shirt and tie, the other in a full suit. When the shot cuts, they have instantly switched sides, and the one who doesn't wear a jacket, suddenly is wearing glasses. (00:05:20)
Factual error: While trapped in the toppling building, our heroes use bundles of computer cabling to keep themselves from sliding out. While bundles of cable are common around the US, they are against code in Chicago, which requires them to be in conduit in a plenum ceiling. Conduits would have easily prevented the bundles from crashing through an acoustic ceiling. And yes, that is a plenum building.
Plot hole: The film tries to claim that all six lunar missions were to collect samples from the Ark. However, the missions had landing coordinates hundreds of miles apart. If only 35 people knew about the secret mission, that leaves hundreds of thousands of others who believed they were working toward actual lunar exploration, meaning it would be very difficult to fake telemetry data without someone noticing. Also, there are long range photographs of the different landing sites showing the landing craft at their true lunar landing spots.
Answer: the weapon is called an "Acid Rust Blaster" which seems to be similar to the cosmic rust seen in the animated series. the rust eats away at the Transformer's metal body.