Besides its many great fights, Dragon Ball is known for its library of transformations. Ever since the original series, Goku was known to transform into a Great Ape, making him a danger to everyone around him whenever he took a single glance at the full moon. As the series progressed, this form was not only utilized by other Saiyans like Gohan and Vegeta, but more transformations were added to the series, strengthening heroes and villains alike whenever they were presented with a significant challenge.
While most transformations present some kind of benefit to the user, there are some that aren't as useful in a pinch. These forms are definitely not as powerful when compared to the transformations possessed by members of another race.
10 Strongest: Androids
From Bio-Androids like Cell to Infinite Energy Models like 17 and 18, Androids are one of Dragon Ball's most diverse races. While their transformations aren't the mightiest in the franchise, it's astounding that some Androids are able to absorb the parts and bodies of their fellow synthetic companions to take their powers to inconceivable heights. While Android 13 didn't seem to be leagues above a Super Saiyan in his base form, he became strong enough to take the attacks of a Super Saiyan without flinching after absorbing the spare parts of Androids 14 and 15 and transforming into Super Android 13.
Likewise, the newest of Dr. Gero's creations, Android 21, could transform into a more powerful form that resembled the phenotype of a Majin. She could also absorb the powers of others to further increase her own. Most notably, after absorbing Androids 17 and 18, Cell was put in a league all his own. In transforming to Perfect Cell, he became so strong that even after self-destructing, he only grew stronger, utilizing abilities that even he had no knowledge of.
9 Weakest: Namekians
Many early Dragon Ball fans might recall that Namekians can grow in size. In the days before flight and energy attacks became the base of what a warrior should be capable of, this transformation was useful for putting the pressure on a regular-sized opponent.
Now, however, a Namekian growing larger would only make them an easier target to nail with an energy attack. Their supersized ears would have no problem picking up on someone's whistling, which Namekians have a natural aversion to.
8 Strongest: Kaioshin
Though they aren't as powerful as Gods of Destruction, Kais have divine abilities all their own, complete with a transformation that's just as aesthetically pleasing as it is domineering. Exceptionally powerful Kaioshin can achieve a Halo form that bestows them with a halo of light that hovers behind them.
Fused Zamasu debuted this transformation during his fight against Goku and Vegeta, and it enabled him to withstand a direct assault from two Super Saiyan Blues all on his own. While the Supreme Kai of Time, Chronoa, isn't much to write home about, her Time Power Unleashed transformation lends her a similar-looking Halo form with power strong enough to completely seal away the Demon Realm as she did in Super Dragon Ball Heroes.
7 Weakest: Zarbon's Race
Readers of Dragon Ball Super's manga were shocked to find themselves introduced to Yuzun, another member of Zarbon's race. Similar to Zarbon, Yuzun clearly paid attention to his physical appearance; however, when faced with a strong enough opponent, he was forced to tap into a transformation that instantly gave him greater physical strength and a face that only a mother could love.
While this transformation is useful in dire moments, members of Zarbon's race are so vain that they often hesitate to adopt it. The extra size also slows them down a bit, and the boost in strength isn't as impressive when compared to the boost lent by similar transformations utilized by other races.
6 Strongest: Majins
Out of every other major Dragon Ball Z villain, Majin Buu went through the greatest amount of physical alterations due to his transformations that were spurred whenever he either absorbed others or they managed to escape his body somehow. Depending on who he absorbs and how powerful they are, his physical appearance, personality, and fighting style changes, which means that Majins have the potential to be the strongest race in the entire series if they were ever fortunate enough to absorb God of Destruction-level characters.
In Xenoverse 2, every Majin was able to transform into a Pure Majin. Similar to Kid Buu, they retained his agility and reckless fighting style that made him more of a danger than when he'd absorbed fighters like Piccolo and Gohan.
5 Weakest: Earthlings
Sure, Earthlings can utilize the Kaio-ken, and some, like Tien, can sprout two additional arms, but these aren't transformations but techniques. So far, Master Roshi is the only Earthling to debut an actual transformation similar to the ones seen in other races. His Max Power transformation not only grants him pounds of bulging muscle, but it also enables him to utilize ki-based attacks to their fullest potential. It's often been his ace in the hole during his most harrowing moments. It gave Roshi's Kamehameha the boost it needed to defeat Ganos during the Tournament of Power, and it came in handy when he was forced to destroy the moon after Goku transformed into a Great Ape during their fight at the 21st World Martial Arts Tournament.
Other races, like Frieza's and Saiyans, have similar transformations that increase their strength and lend them similar physiques. However, the major disadvantage is that these hulking forms throw speed to the wayside, not to mention the massive energy drain that they impose upon the user.
4 Strongest: Frieza Race
During his fight on Namek, Frieza tormented the Z-Fighters as he went through four unique forms, showcasing different techniques and fighting styles with each. It seems like Frieza's people have an endless amount of transformations under their belt, with Cooler even debuting a fifth form during the movie Cooler's Revenge.
In Dragon Ball Super, Frieza managed to unlock, and perfect, a new Golden Form. This allowed him to spar with god-level opponents despite previously being no stronger than a standard Super Saiyan when he was first resurrected. It's safe to say that if Frieza manages to discover an extra transformation on top of his Golden Form, he may become stronger than any other character in the franchise.
3 Weakest: Yardrats
The Yardrats aren't really fighters, but they still had to come up with practical techniques to help them survive in such a cruel world. One of them is a Gigantification transformation that increases their size using Spirit Control.
The transformation doesn't do much to bolster an individual's power though, making it more useful for intimidation rather than for battle.
2 Strongest: Saiyans
Whenever they're pushed with a new challenge, Saiyans' bodies almost seem to adapt, and a new transformation just comes from nowhere to help them. This happened when both Goku and Gohan found themselves backed into corners in their respective battles against Frieza and Cell. After learning how to manipulate god-ki, Goku and Vegeta found out how to channel this divine energy into their Super Saiyan transformations, thus giving them the insanely powerful Super Saiyan Blue form.
Despite their transformations already being so powerful, it seems as though Saiyans have only scratched the surface of what they can become, with Vegeta's new Super Saiyan Blue Evolved transformation taking his powers beyond their limit once more.
1 Weakest: Caterpy's Race
Dragon Ball Z's Other World Saga might be completely filler but it gave fans the legendary duel between Goku and Pikkon. But before this battle came the one between Goku and the Universe 7 Southern Quadrant warrior known as Caterpy. During their fight, he went into a state of metamorphosis, and it was revealed that he'd come out of it in his ultimate form.
The biggest downside is that this transformation takes 1,200 years to complete. Even if it gave Caterpy powers to rival Zeno himself, the fact that it takes so long makes it useless, since no serious opponent would wait 12 centuries for it to finish.