In the beginning of the movie, at the the end of Keno's first fight, his line "Stay Down" was improvised. See more

Goofs

Before the final fight with Tokka and Rahzar, when Donatello and Professor Perry deduce that they need CO2 in order to destabilize the mutation, they find a fire extinguisher. When they grab it, you can see from the pressure gauge that it is in fact not a CO2 extinguisher. This would make sense because CO2 extinguishers are primarily used for closed in areas or electrical equipment. See more