The following is a map by amateur forgist, MSSZero159.
BACKSTORY:
You are a veteran ODST. In the year 2612, you went for a routine pod drop. As you descended, a Blue Fuel Covenant blast took your pod by force, knocking you out.
You wake up, approximately two days later. You are stranded in an arctic tundra, alone, with only the emergency supplies from your drop pod and the forest of possibilities lying near.
Three years have passed. You have built a fort using the supplies you could find lying around. Days pass, and somehow, the cold surroundings decrease even more in tempature. You start to fear, because of the decreasing tempatures, that you may inevitably die of frostbite.
You have one objective. Survive.
MAP:

(Above) The main base of ODST's Downfall.

(Above) Two of the sub-bases, equipped with ve-hicles.

(Above) A glimpse of the main base, from an eagle eye view.

(Above) Another bird's eye view of the main base.

(Above) Two more sub-bases. Less ve-hicles, more power-ups.
DOWNLOAD ODST'S DOWNFALL RIGHT HERE!
GAME:
There are two versions of the game for Downfall.
"Frostbyte"
Frostbyte is the original version of the game for Downfall. Zombies die in one hit, humans take a little more effort to kill. Humans spawn with an SMG and a shotgun. The Alpha Zombie spawns with the inability to use vehicles, the ability to trade switch weapons, and a 25 meter radar. The "frostbitten" zombies spawn with all of the same stats, except they have no radar, but can drive vehicles.
DOWNLOAD FROSTBYTE RIGHT HERE!
"Frostbyte (Helljumper Edition)"
This is Frostbyte, except the human spawns with the stats you have in the campaign for Halo 3: ODST. They spawn with an SMG and a Magnum, can take only 90% of the normal damage, and they have no shields. The other downside to this is that there is absolutely no way to get your health back, unlike in the upcoming Halo 3: ODST, there are MediGels one uses to restore their health. THIS VERSION IS RECCOMENDED FOR HARDCORE HALO 3 PLAYERS ALONE!! No lie, this is extremely challenging.
DOWNLOAD FROSTBYTE HELLJUMPER EDITION HERE!
Thank you for reading, and/or downloading, and enjoy!
-MSSZero159