CheatCodes.com has the complete list of all Serious Sam: The First Encounter HD Achievements and Gamerscores for X360, including all secret Achievements. All official X360 achievements for Serious Sam: The First Encounter HD as of Wednesday September 2, 2015 are shown below, or you can print out our Printable Achievements Checklist that shows all Serious Sam: The First Encounter HD Achievements and Gamerscores in a simple quick-reference format.
Complete any level in single player.
Complete the game.
Complete the game in single player on serious difficulty.
Complete the game in single player without firing a single bullet or shell.
Complete the game in single player by beating estimated time on each level.
Complete Metropolis level in single player on serious difficulty without loading.
Pierce at least 10 enemies with a single cannonball.
Kill all enemies in Karnak in single player.
Find at least 50 secrets in single player.
Complete any level in co-op.
Complete The Great Pyramid in co-op with blood option set to hippie.
Complete a co-op game on serious difficulty and extra enemy strength on 400%.