Vidmaster Challenge: Déjà Vu
From Halopedia, the Halo wiki
Deja Vu is an achievement in Halo 3: ODST and one of the Vidmaster challenges. It is unlocked when you complete Highway (Firefight) on 4-player Legendary Live co-op, with Iron skull activated, and not using the Warthog or Scorpion at all. It is worth 25 Gamerpoints.[1]
