HT Games
Took The Highway Trophy
Beating "Highway to Hell" on any difficulty will earn the player the "Took The Highway" trophy. This is a Bronze trophy, and can only be obtained by completing this level.
Extra Difficulty Levels
Beating "Highway to Hell" completes the game, which will unlock different difficulty levels depending the original difficulty you beat it on. In order to unlock the "Morbid" difficulty, you'll need to beat the game on "Grim" difficulty. Unlocking "Undead" difficulty will require you to play through once more and complete the game on "Morbid" difficulty.
Bronze End-Game Trophies
There are several Bronze trophies that can be obtained by the end of the game, depending on how you've played throughout the course of the game. These include "Blown to Bits" for blowing up 1,000 zombies, "Car Killer" for destroying 500 vehicles, "Contributor" for helping your country clear the virus infection, "Easy Does It" for beating the campaign on "Braindead" difficulty and "Pyromaniac" for burning 1,000 zombies. Other Bronze trophies include "Suit Up" for collecting an armor piece, "Survivor" for clearing a mission without dying, "Teamwork" for completing a mission in Co-Op mode on any difficulty, "Up Close & Personal" for performing 500 melee kills, "Upgrader" for fully upgrading a single slot on any weapon in Campaign mode, and "Zombie Killer" for killing 1,000 zombies.
Silver End-Game trophies
Players can also earn a number of Silver trophies by the end of "Highway to Hell" depending on their performance throughout the game. These include "Aim For The Head" by performing 500 head-shots, "Looter" for collecting all the loot in any mission, "Mediocrity" for completing Campaign mode on "Normal" difficulty, and "Skilled" for completing a mission without taking any damage. Other Silver trophies include "Tough Enough" for completing Campaign mode "Grim" difficulty, "Very Dead" for completing Campaign mode on "Undead" difficulty, "Weapons Specialist" for fully upgrading all slots on any weapon in Campaign mode and "Zombie Hunter" for killing 10,000 zombies.
Gold and Platinum End-Game Trophies
Beating "Highway to Hell" can also unlock some Gold trophies or even the Platinum trophy depending on your performance throughout the game and the difficulty level. These include "Double the Action" for completing the Campaign in Co-Op mode, "Genocidiary" for killing 53,596 zombies, "King of Looters" for collecting all loot in every mission, "Morbid Curiosity" for completing Campaign mode on "Morbid" difficulty, and "Top Gear" for collecting all armor pieces. The Platinum trophy "Romero Would Be Proud" is earned by collecting all other trophies.
Zombie Dance Easter Egg
After the first Weapon Shop, take to the road to the right that winds it's way behind the blue buses. You'll find an area with a pen containing several zombies. If you approach the pen, the music will change and lights will begin flashing. Then the zombies in the pen will dance until you kill them.