Here is the full list of all 42 Serious Sam Classics: Revolution achievements.
Kill 100.001 enemies.
Kill 5000 marsh-hoppers with the chainsaw.
Finish the Bright Island campaign in single player.
Find Bright Island's second secret level.
Find Bright Island's first secret level.
Kill 50 players with mines.
Finish The Second Encounter on single player.
Kill 100 monsters with mines.
Find a secret Minelayer in The Second Encounter.
Find a secret Plasmathrower in The Second Encounter.
Mess with the gravity for a total of 60 minutes.
Finish the Bright Island campaign in cooperative.
In a match of at least 6 players, run 2 kilometers without getting killed.
Finish The First Encounter on single player.
Deal a total of 1 million damage to enemies.
Find Sacred Yards.
Find the XL4P Beam Gun outside of Bright Island.
Find Moon Mountains.
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.
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.
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.
Kill an enemy player while you're dead.
Find a secret bouncing rock.
Get the gold medal on the Christmas 2014 survival level.
Kill 500 people.
Using explosive weapons, kill 10 people in a row.
Unfortunately, we don't have the right model for it, so this'll do.
Finish The Second Encounter in cooperative.
Kill the boss and complete the Medieval episode.
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.
All Elementals acquired.
Kill the Highlander in Valley of the Kings.
Complete the first Egypt level.
This achievement is impossible to get.