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