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.
Get the gold medal on the Christmas 2014 survival level.
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 100.001 enemies.
Find a secret Minelayer in The Second Encounter.
Find a secret Plasmathrower in The Second Encounter.
Kill 50 players with mines.
Kill 100 monsters with mines.
Finish The Second Encounter in cooperative.
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.
Finish The Second Encounter on single player.
Kill an enemy player while you're dead.
Using explosive weapons, kill 10 people in a row.
Kill 500 people.
Finish The First Encounter in cooperative.
Unfortunately, we don't have the right model for it, so this'll do.
This achievement is impossible to get.
Mess with the gravity for a total of 60 minutes.
In a match of at least 6 players, run 2 kilometers without getting killed.
Find Sacred Yards.
Find Moon Mountains.
Find the XL4P Beam Gun outside of Bright Island.
Find a secret bouncing rock.
Kill the boss and complete the Medieval episode.
Deal a total of 1 million damage to enemies.
Kill the boss and complete the Persia episode.
Kill the boss and complete the South America episode.
Kill 5000 marsh-hoppers with the chainsaw.
Obtain the Crystal Skull.
Finish The First Encounter on single player.
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.
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.