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.
Find a secret Plasmathrower in The Second Encounter.
Find a secret Minelayer in The Second Encounter.
Kill 100 monsters with mines.
Kill 50 players with mines.
Kill 100.001 enemies.
Mess with the gravity for a total of 60 minutes.
This achievement is impossible to get.
Unfortunately, we don't have the right model for it, so this'll do.
Kill 5000 marsh-hoppers with the chainsaw.
Kill the boss and complete the Medieval episode.
Finish The Second Encounter on single player.
Kill the boss and complete the Persia episode.
In a match of at least 6 players, run 2 kilometers without getting killed.
Finish 2 levels in The Second Encounter using only the knife in at least normal difficulty.
Kill less than 8 enemies on the first level of The Second Encounter in at least normal difficulty.
Find a secret bouncing rock.
Find the XL4P Beam Gun outside of Bright Island.
Finish The First Encounter in cooperative.
Finish The Second Encounter in cooperative.
Complete a level in The Second Encounter using only the knife on at least normal difficulty.
Deal a total of 1 million damage to enemies.
Kill the boss and complete the South America episode.
Obtain the Crystal Skull.
Kill 500 people.
Using explosive weapons, kill 10 people in a row.
Find Sacred Yards.
All Elementals acquired.
Finish The First Encounter on single player.
Find the rising obelisk.
Defeat the giant lava golem.
Find Moon Mountains.
Kill the Highlander in Valley of the Kings.
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.
Kill an enemy player while you're dead.
Complete the first Egypt level.