Kirby O'Neil

Kirby O'Neil is the father of April O'Neil. He became a new mutant called Kirby Bat in Season 2 until he was turned back in The Lonely Mutation of Baxter Stockman. He is voiced by Keith Silverstein.

Physical appearance
As a human, he is half blad with still some red hair and a beard. Has has blue eyes with a grey undershirt and a brown jacket. He also has tan pants and brown shoes.

As a mutant bat, he had a large head, a mishapen nose, huge fangs, and large bat wings that have clawed hands. He has tufts of his hair on his lower body and legs with a fluffy tail. His beard still remains. He has a large, green mutagen-filled vein across his head, and a large purple mutagen-filled vein on his torso. His left arm is larger than his right, and his ears resemble bat wings.

Season 1
In Rise of the Turtles, he and his daughter were kidnapped by the Kraang. April was rescued by Donnie, but he was unable to save him.

In The Gauntlet, he send Pete to deliver him the message to his daughter. The message shows that he's telling April that something bad is about to happen, and she must save herself. April still wanted her father back. Even though the Turtles succeeded on freeing him, Kirby had to hold off the Kraang and was recaptured. April sobs, but Donnie promises her they'll get him back.

He was mentioned in TCRI when the Turtles were talking about why the Kraang needed Kirby in the first place. April mentioned her father is a psychologist. He studies rats running through mazes. It is revealed that the Kraang weren't really after Kirby, despite that they captured him. It turns out their real target is April.

In Operation: Break Out, Donnie does his own mission to save Kirby for April. In the detention center, he opened all of the cells to free Kirby, but he unknowingly released an amphibious monster that resembles an anthropomorphic fire belly newt. When he came to greet Kirby and get themselves out of here, they were attacked by the very newt. He begins to attack them with his bracelet blasters that he reclaimed. Donnie believes it resembles some family of Salamandridae if he's not mistaken, though Kirby reveals it's clearly a Pleurodelinae: a newt. Donnie then dubs the creature Newtralizer. When his brothers came to help him and Kirby, Donnie let the Newtralizer destroy the Kraang, much to their joy. However, the Newtralizer targets on them, much to their horror. After Mikey crushed the beast with a car, they all escaped, but the Newtralizer survived. When Kirby arrived in the lair, April is excited to see her father. She thanks the Turtles for rescuing him. In the training room, April hugs her father. However, Kirby has a menacing look on his face without April knowing.

In Showdown, Part 1, it is revealed the Kraang brainwashed him before Donnie rescued him. When the Turtles left, the brainwashed Kirby lies to her that the Kraang have damanged the T-Phones encryption. When April follows him, some Foot soldiers appear and take her hostage. Karai then has the brainwashed Kirby deliver the message to Splinter from the Mousers. When he arrived, Splinter asked where's April. Kirby said that Shredder has a message for him.

In Showdown, Part 2, he attacks Mikey, who entered the training room. The Turtles pile on Kirby and discover the mind control device on the back of his neck. They remove it, and Kirby is feeling terrible of what he did, but the Turtles didn't blamed him. He reveals that Shredder made an alliance with the Kraang and now April is taken hostage. After the Kraang and Foot were "defeated", Mikey asked, "Who's save the world?" a fourth time, which made Kirby, Leo, Donnie and Raph say, "Mikey..." in an annoyed tone.

Season 2
In The Mutation Situation, the long major trauma caused Mr. O'Neil to be protective of his daughter. When the Turtles were fighting the Kraang in the stealth ship, the whole load of mutagen, that was meant to be delivered to the Foot, rain down in the city. One canister was about to fall on April, but Kirby rushes to protect his daughter. He ended up getting drenched with ooze. He then falls off the building and falls past a bunch of bats (which have been under them the whole time). Kirby then mutates into Kirby Bat, much to April's horror. He seems to have lost control of himself as he tries to "attack" April. Begging to not be grounded, she hits his face, making him feel sad. When the Turtles tried to attack him, April stopped them as Kirby Bat takes her away. The Turtles realized that the bat is Mr. O'Neil. April then finds herself on the edge of a building as Kirby Bat arrives back and regurgitates a dead rat and some trash. He smiles, but April is disgusted of her own father expecting her to eat gross stuff. She sends him away so he can get her some real food. Later on, the Turtles uses Mikey as bait to lure Mr. O'Neil. Mikey, in his Turflytle outfit, tries to call him "Wingnut" as a name, but Donnie scolded him for his insensitivity. Once they trap Mr. O'Neil in a warehouse in a cage, Mikey actually gives him the name Kirby Bat. When April learned that the Turtles spilled the mutagen (although it was an accident), she becomes angry at them, even Kirby joins in to blame the Turtles. Kirby Bat then broke out of his cage as he tries to get April, but only for Donnie to hit him with his staff. Kirby Bat then flies away. With Kirby as a mutant, April temporarily breaks up their friendship.

In Fungus Humungous, Kirby Bat appears as a hallucination as April's worst fear, which are bats.

In Metalhead Rewired, Kirby Bat was among the many mutants captured by the Kraang so they can control them. When Metalhead opened all of the cells, Kirby Bat, Spy-Roach, a Squirrelanoid and a Parasitica Wasp discover their cells have opened. While the Turtles were heading for the portal, Kirby Bat was attacked by two Kraang. Luckily, Donnie comes to his aid to save him. He whacks the two alien punks with his bo staff, sending the screaming dorks to their deaths. When Kirby Bat saw them, however, he reacted. Donnie then tells him to fly to the portal for April. Kirby accepts it as he flees to the portal.

In The Manhattan Project (Wormquake!), he is shown as a picture on a tabloid newspaper that April was reading in Kurtzman's apartment.

In The Lonely Mutation of Baxter Stockman, Donnie has created a retro-mutagen to turn him back. In the surface, Kirby Bat sees a picture of a woman on a billboard. He sinks his fangs into her as if he were a vampire. He then takes a rest, while hanging upside down like normal bats. This was the Turtles' chance to turn him back, but only for a mutated Baxter Stockman to snatch the retro-mutagen from them. Kirby Bat woke up and fled. Mikey was then used as bait to lure Kirby Bat. When they knocked him down on a building, April quickly approached her mutated dad. She then tries to calm him down. After that, the mutated Kirby lets April hug him. He then lets Donnie to use the retro-mutagen on him, but it was then stolen back by Stockman. April and Casey then ride of Kirby Bat to get the retro-mutagen back. When Casey fell off, Kirby Bat quickly caught him. Unfortunately, the last retro-mutagen smashes on a lamppost. April steers her father as the last drop of retro-mutagen falls right on him. The Turtles then cover Kirby Bat as he turns back into a human. Kirby's head pops out, and has no memory of being a mutant. April is relieved to see her father again. Kirby asked why was he nude, much to April's shock.

In The Wrath of Tiger Claw, he tried to call April, but he couldn't get her to respond back.

Trivia

 * His nickname is not Wingnut. He's a new character. The Wingnut reference was just a joke. Brandon Auman confirmed that he's one of the new mutants.
 * As a human, Kirby resembles August O'Neil, April's uncle, from the 2003 series.