Cell Jr. is an offspring of Cell. They were asexually produced from Cell's tail, through cellular mitosis. According to Cell himself, each Cell Junior he produced had his power and abilities.
This dropdown contains the synopsis of Cell Jr.’s story. Read at your own risk as you may be spoiled otherwise!
Cell Saga
The Cell Juniors are created during the Cell Games after Gohan tells Cell that when he is angry, his power greatly increases. In order to infuriate Gohan enough to release his hidden potential and provide a true challenge, he has them attack Goku, Vegeta, Future Trunks, Piccolo, Krillin, Tien Shinhan, and Yamcha.
The Cell Juniors are extremely mighty and have strength comparable to Super Saiyan Vegeta and Future Trunks.
They crush most of the Dragon Team without fighting seriously; two of them easily beat on Tien and Yamcha (one of them even brutally and readily breaking Yamcha's arm), another two beat on Krillin and Goku, who is exhausted from his previous fight with Cell. Three of them fight on par with Piccolo, Vegeta, and Future Trunks and inflict considerable amounts of damage, at some points shifting the battle to their favor and slightly overpowering them briefly.
However, after Gohan becomes infuriated by the Cell Juniors' assault on the Z Fighters, coupled with Cell's killing of Android 16, his hidden powers awaken and he transforms into a Super Saiyan 2, allowing him to easily defeat all of the Cell Juniors with effortless blows, shocking the Z Fighters and enraging Cell. Before being taken down, one attempts to stave off Gohan by holding Krillin hostage with the threat that it will kill Krillin should Gohan step any closer or attack it, although this fails due to Gohan's speed in this form allowing him to both save Krillin and evade the Cell Jr.'s attempted attack on Gohan afterward.
In the manga, after seemingly being killed by Gohan, the Cell Juniors managed to regenerate through their intact nuclei, and were tamed by Android 17 to defend Monster Island and not attack rangers.
Super Buu utilized his Human Extinction Attack to kill everyone on Earth, including the Cell Jrs. along with nearly everyone else. While fighting Kid Buu on the Sacred World of the Kai, Vegeta asks Dende to make a wish to Porunga for the Earth and the lives of all its good-willed inhabitants to be restored. The fact that the Cell Juniors were not exempt from this wish is proof of the Cell Juniors inherent goodness after being tamed by Android 17.
Age: 0 years old (They were just born at the time of the Cell Saga), 7 years old during Buu Saga (7 years have passed since the end of the Android/Cell Saga)
Classification: Baby Cell, Mini Cells, Cell-X Jr., Cell's kids
Range:Standard Melee, Interstellar with Ki Attacks (Ki attacks can reach out of the planet and to other planets. All ki attacks should be comparable to Goku's Kamehameha, which reached all the way to the sun)
Intelligence:Unknown Intelligence (Seem to possess a child-like personality but can fight the Z fighters very easily)
Extreme Heats, Extreme Colds, & Air Manipulation (Contains DNA from Goku and Vegeta, who can survive in the Hyperbolic Time Chamber for an entire year, which contains sub-zero temperatures to over one hundred degrees temperatures, along with the chamber having 1/4th the air of the regular world and ten times gravity)
Taunt: Taunting is performed by a user performing some form of gesture, remark, or insult to annoy or enrage their opponent and throw off their thinking.
Blasting Beam: It is an orange energy wave fired from both hands joined together.
Attack Alteration and Redirection: A technique where the user uses their ki to catch an opponents attack, then alters it and fires it again as their own attack.
Face Slap: A physical hit used by a Cell Jr. against Goku. Named in the Dragon Ball Z Collectible Card Game.
Kamehameha: A powerful Ki blast fired with two hands after concentrating a large amount of Ki.
Destructo Disc: A razor-sharp disc of Ki that can slice through almost any substance.
Tri-Beam: This technique is performed by gathering energy, forming a vaguely diamond-shape "tunnel" with the hand's by keeping the fingers on each hand together, overlapping the index finger on the one hand with the pinky of the other hand, and overlapping the thumbs. The object being focused on gets zoomed in on and visualized inside that diamond, then the user shouts "Tri-Beam, ha!" while releasing the large yellow beam from the hands.
Special Beam Cannon: The move is performed by touching the index and middle fingers of one hand to the forehead and charging enough ki to attack. Its speed changes to the power level of the user performing the move. When ready, the fingers are extended forward, and two thin energy beams are unleashed from the fingers. One remains straight while the other coils around the straight beam. The resulting beam is quite powerful, drilling through most targets, and exploding on the ones it can't.
Regeneration: In the Dragon Ball Super manga "Bonus Story 3", it is revealed that after being taken down by Gohan, the Cell Jrs. regenerated. It is suggested they did not became stronger after surviving and regenerating like their father did as their power is around the same level as during the Cell Games though it is unknown if their power increased after surviving near death but diminished over time between the after the Cell Games and the timeframe of the Tournament of Power.
Finger Laser: Cell Jr. can shoot a laser out of his finger.
Other
Standard Tactics: Cell Jr.'s will play around while making their targets suffer and use hand to hand along with ki attacks.
The speed scaling for PLs are taken with a grain of salt as there are noticeable times where someone's speed isn't equal to their power, such as Burter being faster then Recoome and Jeice, along with Super Saiyan Grade 3 Trunks having his power greatly increased but his speed decreased.
Trivia
A slight error was made in the number of Cell Juniors that Gohan defeats in the anime episode "Awakening". If one counts them in the episode, Toei had Gohan defeat eight Cell Juniors, even though Cell only creates seven; this error is not present in the original manga or the Dragon Ball Z Kai redub. However, a possible explanation might be that one of the Cell Juniors used Tien's Multi-Form technique to split in two, and then used the Tri-Beam (which is a technique used by the Cell Juniors only in the anime).
In the dubbed anime, they are said to have the same strength as Cell himself, albeit with substantially less durability (this claim never being made in the manga).
The Tri-Beam is the only attack that the Cell Juniors use that Cell himself is never shown using onscreen. Surprisingly Cell having Tien Shinhan's cells is anime only.
However in Xenoverse 2 after the 1.09.00 Update through Partner Customization, Perfect Cell can be customized with the Tri-Beam Super Skill allowing him to perform it and the Spirit Tri-Beam just like the Cell Juniors. It should be noted that the Xenoverse series tends to follow the anime storyline so presumably Cell and the Cell Juniors both have Tien's cells in the Xenoverse series.
The Cell Juniors, the Bio-Men, and the Saibamen share similarities. All come in groups, are short and about the same height as one another; they each pose a moderate threat at their introductions, but are easily disposed of later. However, unlike the Bio-Men and Saibamen, the Cell Juniors are all able to speak in the anime and one of them has a single line in the manga (like Kid Buu and Evil Buu are in the same series but not the manga), though they do so very rarely (the bulk of their lines as well as their only line in the manga consists of "over here" though they also say the names of their attacks and yell "come get me").
They are also similar to the Meta-Cooler Corps. in that they are essentially duplicates of the original though in the case of the Cell Juniors they are essentially miniature clones of Perfect Cell. Both the Cell Juniors and Meta-Coolers are also related to the Frieza Race and Frieza Clan (as Cooler is the Meta-Cooler's template while Cell Juniors contain Future Frieza and King Cold's cells).
It should also be noted that Cell Juniors, Bio-Men, Saibamen, and Meta-Cooler Corps. are all artificially create lifeforms as Cell Juniors are the offspring of the Bio-Android Cell, Bio-Men where created by Dr. Wheelo and Dr. Kochin, while Saibamen were created by a Saiyan scientist. The Meta-Cooler Corps. are artificial duplicates of Cooler created and controlled by him through the Big Gete Star.
They are also the strongest of the three as they were introduced during the Cell Games, while the strength and durability of Meta-Coolers can be increased through Rebirth thus they could potentially exceed Cell Juniors in strength though unlike the Cell Junior the Big Gete Star is the Meta-Cooler Corps. Achilles' Heel thus the Cell Junior are superior in that they do not have such a weakness.
They are also similar to Medamatcha's Medas which are miniature clones of Medamatcha. Interestingly, in Xenoverse 2 Medamatcha's boss Lord Slug wishes to acquire Cell Juniors for his army or at least technology capable of creating Bio-Androids like them.
Since they live on Earth in the Dragon Ball Super manga after it was destroyed by Kid Buu, they presumably were not evil at the time (presumably having been tamed by Android 17 by that point) or being children were never really evil as they were simply obedient and loyal to their father.
Android 17 taming them may be influenced by the fact Android 17 was part of Cell when they were birthed, thus they and/or Android 17 may feel a certain kinship to the other. Alternatively, they follow Android 17 as he is a fellow Android (Bio-Androids are a type of Android) .
In video games (Super Butōden 2, the Budokai series, the Budokai Tenkaichi series), a blue Cell Jr. palate swap can be used as an alternate version of Cell in Duel, Practice and World Tournament mode.
Though there is no actual Cell Junior recolor in Xenoverse 2, after the 1.09.00 Update Cell (Perfect) can be color customized allowing players to change his carapace color to resemble Cell Junior's color scheme.
In the first Budokai game, Cell's what-if "Cellin" form, shares a similar appearance and identical moveset with the nonplayable Cell Jr.: consisting only of Kamehameha, Ultimate Attack, Machine Gun Attack, and Cybernetic Shooter; but with the voice of Cell in his Imperfect form. This implies that Cellin may be a modified version of the Cell Jr. character model made playable for the game's what-if scenario. This also implies that Cell Jr. might have originally been intended to be a playable character.
In the fight of Trunks vs. Mecha Frieza, who is far stronger than his final form, Mecha Frieza immediately goes for his strongest attack, the Supernova. In the original Z anime King Kai even states this is ten times stronger than the power he used on Namek:
Original DBZ Anime Version[160]. The attack is directly noted that it could destroy the planet, but doesn't because Trunks catches it, when Mecha Frieza proceeds to detonate it, the explosion is massive but the planet is still intact, implying Frieza must target the core in order to destroy the planet.
↑"What work do you do on the films, Sensei?
I check the plot and script that gets sent to me from Toei Animation. I also do some character designs and touch-ups, as well as altering the names and such."
