Broly is a Saiyan who was born with an estimated power level of 10,000 at birth. As a new born baby, he sleeps in the same room as Goku with whom he shares his date of birth.Due Goku's constant crying, however, makes Broly develop a powerful hatred against him. He is thought to be killed in Dragon Ball Z Movie #8 after he is punched by the combined strengths of the Saiyans and a Namekian. But he travels to Earth where he is frozen for approximately 7 years. In Movie #10 he is awoken from his deep slumber by Goten's crying which reminds him of Goku crying constantly when they were babies. After a long struggle, he is killed by the combined Kamehameha attacks of Goku, Gohan and Goten. A clone of Broly is made in Movie #11, appearing as Bio Broly. His appearance after he is cloned remains unchanged, but due to the scientists so-called "culture fluid", Broly had received his new appearance, the one that looks like a pile of muck that came to life.
Mind Controlled Super Saiyan
This is the weakest of all of Broly's Super Saiyan forms and is a slave to his father Paragus. Thus, he cannot fully maximize his Super Saiyan potential. This form is awakened by Goku when Broly first sees him in Dragon Ball Z movie 8. However, Broly breaks free of Paragus' control and becomes able to release his full power. This form is used in some video games as his normal Super Saiyan form.
Once Broly is free from Paragus, he can make the full transformation into a true Super Saiyan. This is the same Super Saiyan transformation many of the other Saiyans achieved in the series, granting Broly the usual power and speed increase just like any other Saiyan would receive.
Legendary Super Saiyan
This form is very similar in appearance to Super Saiyan 3rd Grade (Ultra Super Saiyan), but is not the same. In this form Broly's muscle mass increases greatly, but he does not suffer any loss of speed. The form also suffers no problems where energy consumption is concerned. Quite the opposite, Broly actually gains more power the longer he stays in the transformation with seemingly no negative effects, a trait only ever seen in his particular transformation. In Dragon Ball Z movie 8, Broly's hair has a green tint whereas in Dragon Ball Z movie 10, it does not. It is assumed that the green tint was an after-effect of the mind control equipment used on Broly.
(Legendary) Super Saiyan 3
It has been confirmed that Broly will be able to transform from Legendary Super Saiyan to Super Saiyan 3 DB: Raging Blast.