In the original Teenage Mutant Ninja Turtles (1990) film, the turtles facial expressions were cable operated with all the motors, servos etc housed in the shell. In this movie, thanks to a larger budget, the animatronics were much smaller and lighter and were built into the face itself.
Due to backlash from parents over the darker and more violent tone of the first Teenage Mutant Ninja Turtles (1990) movie, the producers decided to not allow the Turtles to use their weapons for almost the entirety of this film.
When the Turtles first encounter Tokka & Rahzar, Michaelangelo asks, "Didn't we see these guys on WrestleMania?" In fact, Kevin Nash (Super Shredder) would later make five WrestleMania appearances; including one as WWF Champion at WrestleMania XI (1995).
Starting in this film, Paige Turco takes over the role of April O'Neil. Turco bares more a resemblance to the character as she's seen in the original Mirage comic book. The original Teenage Mutant Ninja Turtles (1990) actress, Judith Hoag, was never even approached about the idea of reprising her role from the first movie, and she blames it on her own personal complaining - particularly about the six-day schedule and the amount of violence in the movie.
The abandoned subway station, which serves as the Turtles' new lair, is based on the real life "City Hall" Station of the former Interborough Rapid Transit company in New York City. Although the station itself is decommissioned, the track on which it is located is still active.
In the original comic story, the ooze was made by stranded aliens called the Utroms through a front company called TCRI (Techno Cosmic Research Institute). Since the final script did not include the Utroms, the company was changed to TGRI (Techno-Global Research Industries).
One main concern that Kevin Eastman and Peter Laird had was that the second (and any subsequent) movie stay as much away from the cartoon show, and as close to the original black and white comics as possible, as the first movie did. They felt that there was plenty of material in the black and white books to form the basis for another good movie.
After the original movie had seen unanticipated success in sales of the soundtrack, Golden Harvest committed a $25 million budget for this movie but with principal technology already developed by Jim Henson's Creature Shop, the decision was made to invest heavily in the film's soundtrack. In fact Vanilla Ice has an appearance in the movie performing Ninja Rap and features the Turtles doing a perfectly choreographed dance to it.
Adam Carl replaced Corey Feldman as the voice of Donatello in this movie. According to Feldman, producers did not want him to reprise the role, due to his rehab stint at the time. They had concerns that having Feldman on board would attract negative publicity, clashing with the family friendly image they were trying to portray.
Kevin Eastman and Peter Laird both felt that the Shredder should not appear in the second movie. Laird even planned a scene where a garbage man found Shredder's helmet, crushed and twisted which would have been a subtle enough way to refer to his ambiguous fate from the first film and set the scene for his appearance in a third TMNT movie. However, the producers wanted the movie to be closer to the cartoon and therefore decided to have Shredder return in this movie instead.
Kevin Eastman and Peter Laird didn't want to see Bebop and Rocksteady, or Krang, or any of the other goofy characters from the cartoon show in this and any subsequent movie. However, the studio wanted Bebop and Rocksteady to appear, but since both co-creators were still not in favor of it, Tokka and Rahzar were created.
Though the first movie had exceeded all expectations, Golden Harvest wasted no time green-lighting a sequel because thought the franchise was going to burn out quickly and were surprised it had lasted as long as it did. They wanted to get this movie out in theaters as soon as possible, which is why the film came out less than a year after the first movie's release.
One possible approach that Kevin Eastman and Peter Laird had for the second movie was to use some of the elements in TMNT issue #2 (the Baxter Stockman/mousers story). The Stockman/mousers tale is pretty straightforward, and could've been lifted from the book with little alterations (though they would have to find another assistant for Stockman, as in the movie April already has a different job). Eastman and Laird also wanted to include the Rat King who they felt could be a really neat, visually arresting character on film, and could have some interesting interactions with him, Splinter, and the mousers.
The approach the studio accepted from Kevin Eastman and Peter Laird involve revealing part of the mystery behind the Turtles' origin, that being where the mysterious canister of ooze came from, namely, the Techno-Cosmic Research Institute (T.C.R.I.). The story was to fairly closely follow issue #4 of the comic where the Turtles discover the T.C.R.I. building after a rooftop fight with the Foot. When the Turtles enter the building, they encounter the weird T.C.R.I. aliens (the Utroms - they are little squishy brain-like creatures about the size of a basketball, and ride around in the stomach cavity of their humanoid robot vehicles). The Triceratons were going to appear after the Utroms activated the transmat device they were working on to get to their home. Later they suggested using the whole mouser scenario that is in book 2... only tie the mousers in with the T.C.R.I. guys - they created the mousers. Baxter Stockman is actually a T.C.R.I. alien, fronting his mouser idea as a way of making money for the company, to aid their efforts to get off the planet. The studio used this as the basis for this movie made changes to closer resemble the Fred Wolf cartoon show. Among them was replacing the Utroms, Triceratons, and Baxter Stockman with the Shredder, Tokka and Rahzar, and a cartoon Baxter knock off named Jordan Perry.
In the scene where the turtles are leaving Aprils house and sneaking into the sewer to find a place to live. Before Michelangelo goes into the sewer the line he says to April is a quote from Humphrey Bogart character in Casablanca (1942).
The trivia items below may give away important plot points.
When Vanilla Ice (who has a cameo in this movie) first arrived on the movie set, Michelan Sisti (the actor in the Michaelangelo suit) went up to Vanilla Ice to give him a hug and welcome him aboard on the movie. However, Ice's overweight bodyguard stiff armed him - even with the full Turtle suit on - and nearly eighteen of the actors and stunt men, including Dan Pesina, stepped forward to pounce and defend Sisti. The film's stunt coordinator, Pat E. Johnson, immediately stepped in and stopped them from fighting. Pesina later told the incident in an on-line interview and said that, "[Vanilla Ice's] bodyguards almost got their butt kicked."
In the original script, the film was to end on a cliffhanger, with Prof. Perry being revealed to be a robotic shell for an utrom, aliens from the original Teenage Mutant Ninja Turtles comics who created the ooze to power their technology. This was dropped due to the fear of kids mistaking it for Krang, a villain of the Teenage Mutant Ninja Turtles (1987) cartoon series who was based on the utroms.
At one point during the club scene with Vanilla Ice performing, Leif Tilden (the actor in the Donatello suit) was supposed to roll stuntman Dan Pesina (a Foot Soldier) and then do a side kick like choreographed. However, Tilden decided to do a roundhouse kick instead without first telling Pesina, and as a result, Pesina almost had his two front teeth knocked out.