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