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