When Nino's home is raided, it's supposed to be morning, but during one of the break in shots, it's night time (you can even hear crickets).
When Nino stabs Kareem, the dagger is in Kareem's hand in one shot, but next to his hand in another.
When Nino, and G-Money are on the roof, they hug each other. You can see tears coming down Nino's face, but after Nino pushes G-Money away and pulls out the gun the tears are gone.
When Nino Brown kills the first cop in the second bust, we see he removes the cop's hat and puts it over the cop's face. When he killed Park, we can see that Brown is wearing the same cap.
When Needles comes to the club on New Years Eve, Nino pulls a knife and cuts off Needles ponytail. The ponytail comes loose an inch above the blade of the knife when Nino pulls on the ponytail before he moves the blade.
During the wedding scene, the two cops break into Nino's safe to steal computer discs. Any evidence gained directly or indirectly from these would be tossed out of court as inadmissible as the result of a (blatantly) illegal search, under the 4th Amendment.
"Pookie" is be blinking during the bomb defusing scene, even though he is supposed to be dead.
Obvious dummy hand when Nino stabs Kareem.
At the beginning of the movie, while coming up to the bridge you can hear the news report that Don Armeteo has been gunned down along with other members of his crew. That does not happen until much later in the movie.
In the beginning of the film where the credits were being rolled along with the New York Skyline, The World Financial Center did exist in the year 1986, but much of the commercial complex was under construction as well as Battery Park City. Two World Financial Center (the building with the round dome rooftop) was under construction at that year and didn't finish completion until 1987; one year after the time setting.
When the CMB is taking over the Carter Projects by force, the man who gets shot by an Uzi-toting thug while defending his family has holes and blood on his back before the sound of the gunfire is heard.
Just after Scotty are being talked into having Nick in his team, Nick fires his gun creating a pattern of a smiley face onto the wall - but only six shots are heard being fired, and the smiley consists of seven holes.
When Duh Duh Duh Man Is holding the guy off the bridge in the beginning you can hear the helicopter that is filming the scene.
During the opening scene when the helicopter is zooming in the Duh Duh Man Holding the drug user upside down from the Queensboro bridge, You can Clearly see an NYPD boat right below it waiting for the stunt double to fall into the East river.
Pookie's time inside the Carter was extensively videotaped, and those tapes, which included G Money giving the order to kill Pookie after his cover is blown, were all saved by the cops. Despite all that taped evidence that could be used to either convict G Money and several others and/or flip them as witnesses against Nino, the operation is declared a total failure and the tapes are never used.
Boom mic shadow on Scotty's hat on the beach.
No cop would show up to testify at a trial with sunglasses on and put his feet up on the front of the witness stand, as Scotty does in the closing court scenes. Officers who testify are instructed to come in suits and don't sit like they're in their basement watching TV.