For regular trainers use the VS Seeker. You cannot re-battle the gym leaders though. You can battle Cheren in Victory Road and Bianca in Juniper's Lab.
You cannot rebattle Gym Leader in Pokemon White.
You cannot rebattle legendary pokemon. (Correction, Giratina is on Platinum ONLY)
No, however, in Pokemon Platinum, it is possible to rebattle gym leaders at the Survival Area.
No
Yes, you can. I have no code, but try a Google search.
you'd need a rebattle reggigias cheat from action replay if you have one.
No
yes. you can rebattle all legendary Pokemon. you just need to defeat the Pokemon league first, and they will come back to life.
The elite four, the champion, (Cheren, Bianca,you have to find them)and,(Cynthia,after you beat the game)
Okay. insructions: 1) upgrade your Pokemon black/white to version 1.2.0 2) talk to Cynthia in undella town 3) Go to the gyms and battle away :)
no you can't
If you killed Virizion, don't save! Turn off the DS and go back. If you save, he will not come back.