Continuity mistake: When Stallone stops the bad guys in the semi full of cocaine, they fly through a windshield that is apparently made of plate glass, and not the safety glass found on almost every other vehicle windshield on earth.
Continuity mistake: When Tango and Cash are playing the "good cop, bad cop" routine with Requin, the tape on Requin's mouth is almost off, but in the next shot the tape is OK.
Other mistake: Their big 4x4 at the end is really a two wheel drive. When they make the big jump with the fire all around them you can see the front end in the light. There is no front differential, just two big A frames.
Continuity mistake: When Stallone catches Tango with his sister, he sees a stranger (the Chief) in the screen door in the background. He jumps forward into the door taking it with him, along with the stranger. The shot then shows the door get pretty smashed up, falling apart as they both hit the floor heavily. The next shot sees Stallone picking up a perfectly intact door off a crushed Chief.
Continuity mistake: Towards the end of the movie when they are in their big 4x4 destroying the camp, they jump off a small cliff. It is a night scene so they have their headlights on. They cut outside the truck as it jumps and both headlights work. They go back inside, then outside as it does a hard landing. You can clearly see one light is now out from the impact. They go to another inside shot, then outside after it lands. Both lights now work.
Continuity mistake: When Tango and Cash escape from prison, they slide down an electric cable. When Stallone is running to the wire, he has nothing in his mouth. In the next scene, when he jumps to the cable, he has a belt or rope in his mouth.
Continuity mistake: In the beginning of movie, when Cash and Tango's sister are on the couch, she is facing one way. In the next shot, she's facing the opposite way.
Revealing mistake: When Cash stuffs the grenade in the trousers of the guy with the ponytail and throws him down the stairs, you can see that the explosion doesn't come from the grenade but from the hall on the right side of the stairs.
Factual error: In the US (and most other places) ex-police officers and prison guards who are sentenced to a term of imprisonment are never, ever put into the general prison population - they are always put into protective segregation. There are no exceptions and the prisoner cannot request that they be not segregated - it just does not happen.
Revealing mistake: When Tango and Cash hold a bad guy upside down off a roof, Tango has his arms straight out in front of him, elbows locked, parallel to the ground. This would require incredible strength. In the next shot he holds the bad guy properly, held close to his own body with his elbows bent - but Tango appears to be exerting no effort in order to lift the guy at the beginning of this new shot. We can also see the outline of a harness system to hold the bad guy up under the black silk shirt of the bad guy.
Revealing mistake: When Tango and Cash are getting attacked down the laundry chute, they are tied up above a water tank with a guy holding an electric wire. Their hands are tied to dry cloth which is then tied to the cable. Cloth has no conductivity so there is no complete circuit when their feet are lowered into the water so they wouldn't be getting shocked. The reason they wouldn't be getting shocked is actually explained later in the movie just before they slide down the electric wire.