Here is the full list of all 12 JoJo's Bizarre Adventure HD achievements worth 400 gamerscore.
K.O. N'Dool via Perfect in bonus stage.
Down an opponent while they are Stand Crashed.
Win a fight with 22 different characters.
Activate a Blazing Fists match.
Down an opponent while in child form.
Counter a time-freeze.
Raise Mahrahia's magnetic power to maximum level.
Complete Story Mode or Challenge Mode for any character on any difficulty without using continues.
Down an opponent without using a Super Combo or Tandem Attack.
Upload replay data.
Down an opponent with a Super Combo.
Win one Ranked Match over Xbox LIVE.