From The TimeSplitters Wiki

Day of the Dammed
Game	TS2
Section	Behead The Undead
Map	Siberia
Character	Nikolai
Enemies Encountered	Feeder Zombie Lt. Chill ?
Rewards	Silver: Feeder Zombie
Medal Requirements	Bronze: 10,000 points Silver: 15,000 points Gold: 20,000 points Platinum: 25,000 points

The Day of the Dammed mission involves controlling Nikolai who gets trapped in a room in Oblask Dam and gets attacked by zombies. There are no weapons in this challenge except for your Fists.

Strategy

This challenge's objective is the same as the other Behead The Undead challenges: kill zombies with headshots and retain your health each round for points. The only difference this time is that you're unarmed, with only your fists to fend off the oncoming waves of the undead. The strategy here is to simply run forward and hit the zombies in the face one at a time. This will work for a couple of rounds. Eventually, faster zombies will attack and this will make this strategy less effective. Circling around the zombies while punching them works well. Make sure not to get cornered! Also, try running forward when the zombies are all grouped together and quickly back off when they try to strike you. They will end up hitting each other and killing fellow zombies by knocking each other's heads off.