The Big Trilogy is a popular title given to the three final season 3 episodes of the 1987 TV series.
The trilogy begins with the episode The Big Rip-Off, when Technodrome is located near the core of the Earth. By tricking the Turtles, Krang, Shredder, Bebop and Rocksteady manage to repower the Technodrome and bring it to the Earth's surface.
In The Big Break-In, Krang launches his Minimizer, shrinking military bases, before the Turtles manage to use the Minimizer to shrink the Technodrome. However, Krang is able to use the technology of the Technodrome to reserve its effects.