Dragon Ball Transformations and fusions
The transformations and absorptions
The Saiyan transformations
All saiyans can transform into Oozarus (Great Apes) when they look directly at the full moon.
The false Super Saiyan transformation is used only by Goku when he fights Slug in the "Lord Slug" Movie.
The Super Saiyan transformation is used by Goku, Vegeta, Bardock, Gohan, Goten, Trunks and Broly.
The transcended Super Saiyan transformation is achieved by Vegeta and Future Trunks in the Cell saga. It is an intermediate transformation between the SSJ1 and the SSJ2 state.
As for the SSJ2 transformation, it is achieved first by Gohan during the Cell Sage and then by Goku and Vegeta.
The Legendary Super Saiyan form comes next and it is only achieved by Broly. This transformation is superior to the SSJ2 transformation since in the movie "Broly the Second Coming", LSSJ Broly defeats SSJ2 Gohan before SSJ2 Goku, SSJ2 Gohan and SSJ1 Songoten defeat Broly with a combined Beam Attack.
In the Dragonball manga and anime serie, only Goku can transform into a SSJ3.
Then, in Dragon Ball GT, both Goku and Vegeta transform into Super Saiyan 4s. For Vegeta, he managed to become a Super Saiyan 4 with Bulma's help while Goku can transform freely into this form.
And next comes the Super Saiyan God form which is a special transformation which requires the power of 6 pure-hearted saiyans.
And finally, the blue super saiyan transformation which is how look saiyans characters when they have god ki. This new transformation is seen in the DBZ Movie "The Revival of Freeza".
The Frost Demon transformations
Cell's absorptions and transformations in Dragon Ball Z
Baby's transformations and bodies' possessions in Dragon Ball GT
Baby is a parasite life form the anime Dragon Ball GT. He possessed Vegeta and others saiyans characters but in the serie is main host was Vegeta :
Ginyu's Body Exchanges in Dragon Ball Z
With his special ability, Ginyu can swith his body with his opponent like he successfully did in the Namek Saga with Goku and tried to do with Vegeta later in the story arc :
Others transformations in Dragon Ball
The Dragon Ball Fusions
Here are all the fusions found in Dragon Ball, DBZ and DBGT as well as the What-If fusions found in derived fan-made works such as Dragon Ball AF or created specially for some Dragonball Z video games such as Dragon Ball Z Budokai 2 :