Spike

Spike (now called Slash, for now) is Raph's former pet turtle, who transformed himself into a mutant turtle. He is voiced by Corey Feldman.

Physical appearance
Spike first started as a common box turtle.

As a mutant, he is anthropomorphic turtle with spikes on his shell (even the front) and his skin. He has teal scales with sharp nails and massive foot claws. He is bulky and wide, and his mouth resembles the beak of a snapping turtles as they are lined with teeth. He now wears a black mask, belt, straps, and wears a belt buckle.

Early life
Raph saved him when Spike was flushed down in the sewers from a toilet. Raph has often feed him lettuce leaves and gives him a ride of his shoulder. He tells Spike about important parts of his life in private. He could not reveal his feelings to his brothers because he doesn't want to seem "soft" toward them, so he shares them with Spike, who could not speak at that time, but was an excellent listener. His brothers sometimes tease him about this, which makes Raph want to teach them a lesson.

Season 1
Spike's very first appearance was Rise of the Turtles, Part 2. Raph was telling him about his feelings and saying he will come back. Spike listens, while eating a lettuce leaf. Mikey begins to tease Raph, who proceeds to attack his brother.

Spike makes his second appearance in Turtle Temper. After Raph was sent home for his bad temper, he tells Spike that being angry makes him strong. When Raph told him to chew on his leaf if he understands him, Spike does so. When Splinter asked Spike to chew on his leaf if he's in the mood for a story, he does so.

In Panic in the Sewers, after Leo sawed that Raph turned on the TV (which had Space Heroes on), he tells Leo that it was Spike's idea. He said that Space Heroes is too stupid for him. Leo said it was saying something, considering he hangs out with Raph all day. Raph becomes mad at Leo, who apparently made Spike angry. He decides to mop the floor with Leo's face.

In Karai's Vendetta, Raph feeds Spike a lettuce leaf, while they watch Space Heroes.

In Operation: Break Out, he gives some popcorn to Spike.

In Showdown, Part 1, Raph gathers his weapons and items he needs for the showdown. Before leaving, he gives Spike a pet on the head.

In Showdown, Part 2, when they returned to the sewers, Raph shouts out for Spike because he is worried something bad happened to him. However, Spike is safe and sound as he reveals he's on the sofa. Raph picks him up and places him on his shoulder, telling him to not scare him like that. He then gives him a first bump with his finger. After the showdown, Spike is seen standing on the record player.

Season 2
In Slash and Destroy, Spike makes his first introduction appearance as a mutant. After Donnie's accident went wrong, one explosion almost hit Spike, but Raph saved him. Blaming Donnie for this, he takes the last canister of mutagen to his room. He tells Spike that his brothers hold him back, and doing stupid things rather than tracking mutagen. He says to himself that he wants to do things his way. After he was summoned to help, the mutagen canister breaks! Spike the mutates himself into a mutant turtle. When Raph arrived back to his room, he discovered the broken canister and a mutated Spike. He is amazed by this, and Spike tells him that they'll team up together, crush their opponents, find mutagen and not goof around. After Spike armed himself and chose his weapon, he tells Raph he never liked the name Spike. He tells him that he wants to be called Slash. It is revealed that Slash has developed a vendetta on his brothers (saying that if Raph's going to be free, they may need to lose some "dead weight"). When Leo and Raph argue of not getting the mutagen, Slash sneaks behind Donnie and attacks him. Later, he arrives back with Donnie's mask in his right hand. Mikey then discovers this and is frightened. Slash tells him that they don't need them and will hunt the mutagen down now. When Mikey begs to find Donnie, Raph apologizes to Slash that his brothers come first, no matter what, much to his disappointment. When he makes the choice a little easier, he pounds Mikey on the ground! Raph pushes him away, but Slash doesn't want to fight him and tells him to leave. Raph tells him that this isn't him and calls him his original name. Slash tells him his new name is Slash (which he told him). He proceeds to kill Mikey, but Raph stuns him with a ninja smoke bomb, giving him and Mikey a chance to escape. However, when Mikey hears Leo's voice, he approaches the figure at an alley. However, the figure reveals he's Slash! He attacks Mikey and takes his mask, too. Raph is enraged of Slash trying to kill his brothers and asked why was he doing this. Slash tells him the others hold him back, and tells Raph to limit his potential and doesn't need them (just like he said). Raph, however, told him he never wanted this. Slash says there's no turning back now. Before he could kill Mikey, Raph tells him to stop and won't let him hurt him. Slash tells him he's not here to fight him. Raph says he wants to, and begins to tell him he's not Spike, but some kind of worth monster (a deranged, hideous freak). Slash is angered and fights Raph. They then broke into a little girl's apartment (which Leo had to have a tea party with her). Slash tells him that he lost, and saying they're both the same. Raph declines it, and tells Slash he's pure evil. Slash roars with anger as he bruises Raph. When Leo arrived to help, he is also injured by Slash. He said he's been looking forward to that for a long time. Raph tells him it's over, to which Slash agrees that they're not like the others, and telling them they're weak, while he and Raph are powerful and their anger makes them strong. He tries to swipe Raph, but he hits his pressure points, stunning him with pain. He gets the masks back, but Slash is about to fall off the edge! Raph shouts with horror as he quickly tries to save him and calls out his original name. However, he fails as Slash falls off the building and crashes on the ground, believed to have died. However, the Turtles discovered he survived and has vanished. But he's still out there, somewhere.

In Metalhead Rewired, Slash is one of the detained mutants captured by the Kraang in order to control them. He is discovered by Raph as Slash is shown in a cell before being brainwashed. After Metalhead freed him from the control and released him, Slash quickly beats up every Kraang as Rockwell, Newtralizer, and a Squirrelanoid escape. During the fight, he saved Raph from a Kraang and nods respectfully at him. He then escapes with Pete and Spider Bytez.

In Newtralized, he ended up captured by the Kraang again, but he is saved by the Newtralizer. He introduces himself, but couldn't understand the Newtralizer until he translate his translator to English. He then joins the Newtralizer to destroy the Kraang at any cost. They then call each other brother. He then meets Raph again and this time he's with Casey. He reveals his new partner and they both take out the Kraang. They escape with teleporters powered with plutonium. In a warehouse, they both take out two Kraang. Newtralizer says they first find Kraang communications then blow the place to "rakka, rakka, rakka, rakka". However, Slash declines it as it's too dangerous and asks him about the humans outside on the streets. Newtralizer then reminds him the day they met. When the Turtles battled Slash and Newtralizer, the mutant/alien newt sets an explosive discs as he and Slash teleport, while the heroes escape the explosion. It is revealed that Donnie put a spy-roach on Slash during combat. By using his roach, they can listen to what they're talking about. Newtralizer reveals the Kraang are testing their new weapon at the docks at midnight. He plans to use to wipe out the Kraang and destroy the whole city. Slash, however, knows it will take every innocent human with it. He scolds at his idea as Slash is here to take out Kraang, not people. However, Newtralizer does not care for people. At the docks, he tells Slash to distract the Kraang, while he pilots the walker, which Slash questions him that he has to trust him inside it. Newtralizer tells him he knows how to pilot and he doesn't have a choice, much to Slash's anger of is carelessness. During the fight, Newtralizer almost crushed Spike, but Raph saved him as they both got out safely. Slash is glad of how Raph saved him, but the Newtralizer continues to attack. Slash teleports to the walker and tries to convince the Newtralizer that the Turtles helped them fight the Kraang. However, the Newtralizer doesn't care. Fed up of his carelessness, he traps the Newtralizer's tail, making the mutant newt angry at his betrayal, but Slash says he's no brother of his. Just as Newtralizer was about to shoot him, Raph throws a shuriken at his teleporter. As he lands, Newtralizer knocks them both off the walker. Luckily, Casey defeated the Newtralizer. Raph is glad that Slash is good, and says there's always room on the team for one more. Slash, however, respectfully refuses the offer and prefers to be better off solo. He says goodbye to them and will see them all again someday. He then teleports away.

Raphael
As his pet, Raph was best buddies with him and talks about his feelings. He gives him lettuce leafs for him to eat. Now as a mutant, he wants to be with Raph without his brothers and plans to get rid of them. However, after being saved, Slash becomes good again, but he prefers to be solo.

Turtles
When he became mutated, he developed a vendetta on them for thinking they hold Raph back. By then, he now develops respect for them for helping them fight the Kraang.

Newtralizer
At first, they were good partners on stopping the Kraang, but they turned on each other after Slash sees that Newtralizer doesn't care for people and the Turtles.

Trivia

 * Slash is voiced by Corey Feldman, who voiced Donatello in the first and third live action film.
 * The belt buckle is actually an old car hood ornament.