Here is the full list of all 42 Serious Sam Classics: Revolution achievements.
Find Bright Island's first secret level.
Finish the Bright Island campaign in cooperative.
Finish the Bright Island campaign in single player.
Find Bright Island's second secret level.
Kill 100.001 enemies.
Kill less than 8 enemies on the first level of The Second Encounter in at least normal difficulty.
In a match of at least 6 players, run 2 kilometers without getting killed.
Get the gold medal on the Christmas 2014 survival level.
Kill 500 people.
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 monsters with mines.
Kill 50 players with mines.
Kill 5000 marsh-hoppers with the chainsaw.
Mess with the gravity for a total of 60 minutes.
Kill an enemy player while you're dead.
Using explosive weapons, kill 10 people in a row.
Finish The Second Encounter in cooperative.
Find Sacred Yards.
Find Moon Mountains.
Find the XL4P Beam Gun outside of Bright Island.
Unfortunately, we don't have the right model for it, so this'll do.
Find a secret bouncing rock.
Find a secret Minelayer in The Second Encounter.
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.
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.
Finish The First Encounter in cooperative.
Finish The Second Encounter on single player.
Kill the boss and complete the Medieval episode.
Find a secret Plasmathrower in The Second Encounter.
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 on single player.
Deal a total of 1 million damage to enemies.
Find the rising obelisk.
Defeat the giant lava golem.
This achievement is impossible to get.
All Elementals acquired.
Kill the Highlander in Valley of the Kings.
Complete the first Egypt level.