Here is the full list of all 42 Serious Sam Classics: Revolution achievements.
Finish the Bright Island campaign in single player.
Finish the Bright Island campaign in cooperative.
Find Bright Island's second secret level.
Find Bright Island's first secret level.
Kill 100.001 enemies.
Mess with the gravity for a total of 60 minutes.
Kill 5000 marsh-hoppers with the chainsaw.
Kill 50 players with mines.
Finish 2 levels in The Second Encounter using only the knife in at least normal difficulty.
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 Second Encounter in cooperative.
Get the gold medal on the Christmas 2014 survival level.
Kill 100 monsters with mines.
Find a secret Minelayer in The Second Encounter.
Find a secret Plasmathrower in The Second Encounter.
Finish The Second Encounter on single player.
Finish The First Encounter on single player.
Finish the first level of The Second Encounter without jumping in at least normal difficulty.
Finish the first level of The Second Encounter taking no damage in at least normal difficulty.
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.
Find a secret bouncing rock.
Kill less than 8 enemies on the first level of The Second Encounter in at least normal difficulty.
Kill 500 people.
Using explosive weapons, kill 10 people in a row.
Kill an enemy player while you're dead.
This achievement is impossible to get.
Find the XL4P Beam Gun outside of Bright Island.
Deal a total of 1 million damage to enemies.
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 Sacred Yards.
Find the rising obelisk.
Defeat the giant lava golem.
All Elementals acquired.
Find Moon Mountains.
Kill the Highlander in Valley of the Kings.
Complete the first Egypt level.