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