Pokemon - I need to trade!

[Golden Phoenix]

Arceus isn't available yet, theres been no event for him, so anyone who has one has hacked it.

Actually, he was given out in Japan.
If you went to see the 12th Movie you could download it to Pokemon Diamond, Pearl or Platinum
It is special and unlocks an event in HeartGold and SoulSilver

Serebii has more details