Here is the full list of all 42 Serious Sam Classics: Revolution achievements.
Kill 500 people.
Kill 100.001 enemies.
Mess with the gravity for a total of 60 minutes.
Kill 5000 marsh-hoppers with the chainsaw.
Get the gold medal on the Christmas 2014 survival level.
In a match of at least 6 players, run 2 kilometers without getting killed.
In singleplayer, beat the last level of The First Encounter or the last level in The Second Encounter in the "I am Ugh-Zan" difficulty.
Finish the Bright Island campaign in cooperative.
Find Sacred Yards.
Unfortunately, we don't have the right model for it, so this'll do.
Find a secret bouncing rock.
Find Moon Mountains.
Finish the Bright Island campaign in single player.
Find Bright Island's second secret level.
Find Bright Island's first secret level.
Find the XL4P Beam Gun outside of Bright Island.
Kill an enemy player while you're dead.
Kill 50 players with mines.
Using explosive weapons, kill 10 people in a row.
Finish The Second Encounter in cooperative.
Kill 100 monsters with mines.
Find a secret Minelayer in The Second Encounter.
Finish The Second Encounter on single player.
Kill the boss and complete the Medieval episode.
Find a secret Plasmathrower in The Second Encounter.
Kill the boss and complete the Persia episode.
Finish The First Encounter in cooperative.
Kill the boss and complete the South America episode.
Finish 2 levels in The Second Encounter using only the knife in at least normal difficulty.
Complete a level in The Second Encounter using only the knife on at least normal difficulty.
Kill less than 8 enemies on the first level of The Second Encounter in at least normal difficulty.
Finish the first level of The Second Encounter taking no damage in at least normal difficulty.
Finish the first level of The Second Encounter without jumping in at least normal difficulty.
This achievement is impossible to get.
Obtain the Crystal Skull.
Deal a total of 1 million damage to enemies.
Finish The First Encounter on single player.
Find the rising obelisk.
Defeat the giant lava golem.
All Elementals acquired.
Kill the Highlander in Valley of the Kings.
Complete the first Egypt level.