The Invasion

' The Invasion' is a two part episode, the Season 2 finale and the 51st and 52nd episodes of the series. They officially aired on television on September 26th, 2014, but were released one week earlier on nick.com as well.

Official Description
Leo and Donnie disagree about their plan to stop the Kraang invasion; Donnie must step up as a leader when Leo makes a mistake and is separated from the team.

Characters

 * Leonardo
 * Donatello
 * Raphael
 * Michelangelo
 * Master Splinter
 * April O' Neil
 * Casey Jones
 * Ice Cream Kitty
 * Kirby O' Neil
 * Irma
 * Karai
 * Shredder
 * Tiger Claw
 * Rahzar
 * Fishface
 * Kraang Prime
 * Kraang Sub Prime
 * The Foot Bots
 * The Kraang
 * Earth Protection Force

Trivia

 * First appearance of Kraang Sub Prime and the EPF.
 * Last appearance of Irma as she revealed to be a robot.
 * The Turtle Mech and The Party Wagon appear for the first time.
 * This the first time The Turtles are defeated and have to flee New York.
 * This is the first time blood was shown, during Splinter and Shredder fight and on Donnie's arm.
 * This is the 4th time Leo has battle damage. He was badly injured in this episode.
 * Also Donnie injured his arm.
 * April's apartment is fully shown for the first time.
 * Leatherhead helps Splinter fight the Shredder.
 * Splinter gets tossed into a whirlpool by the Shredder and is saved by the mutant Karai, though is now separated from the Turtles.
 * April's father, Kirby O'Neil, is mutated (again), this time into a Dimension X creature.
 * Most of New York have been mutated into Dimension X creatures.
 * The Turtles Lair and The Shell-Raiser are badly damaged.
 * Leo is shown getting tossed into April's house through the window (by the Foot Clan). This is what happened in the ending of the TMNT 2003 Series episode "The Shredder Strikes Back, Part 1" and the ending of the Leonardo one-shot from the Mirage comics.
 * Most of Leo's situation while being ambushed is very similar to what happened in the Leonardo one-shot Mirage comic.
 * The year 1984 on the signboard of 'Second Time About...' is a homage to when the Ninja Turtles franchise first started.
 * When Kraang Prime faints, there's a brief appearance of a wind-blown newspaper with an article about a dinosaur man resembling a triceratops as a reference to the Triceratons.
 * The Kraang who find Splinter in the sewer prior to his meeting up with Leatherhead shout "Exterminate! Exterminate!" This is likely a nod to the Daleks of the long-running science fiction series Doctor Who, as Exterminate is their most oft-repeated line. The Kraang and Daleks in their base forms bear some resemblance to each other, both of them appearing as tentacled aliens with prominent brains.
 * There is a Horror and Sc-Fi Film Festival being held in the movie theater, ironic to the events happening in the episode.
 * It is revealed that, in the show's universe, the Kraang were responsible for the human evolution from neanderthals.
 * This is the last time Dominic Catrambone voices Leo, Seth Green takes over the role in season 3.