Form 1: Fat buu
Fat Buu is also called Buu. Buu is very strong evil creation by Babidi. Buu got amazing moves etc.. but hes also very fat O_o.
Buu is like a kid, He eats candy, ice cream, choclate, etc. Buu's face is also very ugly :P.
Nobody wasn't so talented to kill Buu except Goku. Babidi is controller of this creation, but Buu will kill Babidi on Buu Saga.
Form 2: Evil Buu
This is Evil Buu from Good Buu. This is just like Good buu, but he is "evil of buu". Evil Buu is much stronger and faster on this form. Also evil Buu have same clothes as good Buu. Evil buu changes fat Buu to choclate and eat it.
Form 3: Super Buu
Super Buu is evil Buu, but evil Buu is now eated good Buu. This form on buu is incredible, even SSJ3 Gotenks didn't able to stop super Buu. Buu have very nice mucles on this form, also he is very tall. This buu got good Buu inside him, thath's why super Buu have some memories of good Buu.
Form 4: Super Buu + Gotenks
This is just form like others. But this is VERY powerful form. Because this form have power of Gotenks + Buu. Even Mystic Gohan didn't have chance against this form. But this form have one very huge weaknes. Because Trunks and Gohan did fusion dance, it have time limit, 30 minutes. So if Super Gotenks Buu dont beat gohan in 30 minutes he will transform to Piccolo (because he absorbed Gotenks and Piccolo same time).
Form 5: Super Buu + Piccolo
Well, Buu didn't beat Gohan and Goku in time.. So he transformed to Piccolo Buu.. This is the weakest form on Buu.. But Buu will absorb Gohan soon..
Form 6: Super Gohan Buu
This is also very powerful form also. Even Vegito didn't beat this guy.. Buu isnt changed much... He is just much stronger and faster. But he has same clothes as Gohan.
Form 7: Evil Kid Buu
This is "perfect" form on Buu, Evil terror. This form is crazy, Buu destroyed planet Earth on this form. This is really powerful form.. even SSJ3 Goku/Vegeta/Majin Buu didn't have chance against kid buu.
Form 8: Ubuu
After Kid Buu's defeat Goku makes a wish to have him rencarnated as a good person. Uub (Buu spelt backwards) is the result of this wish. We see him fight Goku on the very last episode of DBZ they then go off to Kami's Lookout and train for 10 years.