City At War

"City At War" is the 15th episode of season 4 and the 93rd of the overall. It aired on August 14th 2016.

Official Description
April faces a deadly, new enemy when she graduates to full Kunoichi; the Turtles must deal with the return of some old foes.

Characters

 * Leonardo
 * Donatello
 * Raphael
 * Michelangelo
 * April O' Neil
 * Casey Jones
 * Splinter
 * Ice Cream Kitty
 * Karai
 * Shinigami
 * Tiger Claw
 * Rahzar
 * Fishface
 * Shredder
 * Bebop
 * Rocksteady
 * Baxter Stockman
 * Foot Bot

Trivia

 * First Appearance of Shinigami.
 * This is Mikey's 2nd crush (Shinigami) in the series.
 * The Villains new lair is a penthouse outside the city.
 * Shredder is badly injured and uses mutagen to become Super Shredder.
 * Xever's line, "I am the most interesting fish in the world," is a reference to actor Jonathan Goldsmith, who portrays "The Most Interesting Man in the World" in several advertisements for the beer company Dos Equis.
 * Like Turtles in Time, the episode name references another preexisting part of Turtle lore,City at War, a 13 part storyline in the Mirage Comics; the 2003 series also had it's own story with City at War. However, like the 2003 series, this episode has loose aspects of the storyline such as:
 * Karai looking to restore order to the Foot Clan, though in Mirage, Oroku Saki is dead whereas in Nick, Saki's alive though injured due to the previous episode.
 * A set of followers looking to reclaim the Foot and defeat Karai. The Foot Elite serves this purpose in Mirage whereas in Nick, it's all of Shredder's henchmutants and Baxter Stockman.