Here is the full list of all 26 Serious Sam VR: The First Encounter achievements.
Complete the game.
Complete the game in single player by beating the estimated time on each level.
Complete the game in single player on unmodified serious difficulty.
Complete the Metropolis level in single player on unmodified serious difficulty.
Complete the game in co-op on unmodified serious difficulty.
Pull out a single Colt and immediately deliver a killing shot.
Complete any level in single player.
Trigger Ugh-Zan's regeneration.
Find at least 10 secrets in single player.
Leap into the unknown on Luxor.
Kill 300 Enemies with the Minigun.
Kill 20 enemies with the Minigun without releasing the trigger.
Defeat the Lava Golem boss.
Kill 100 Enemies with the Cannon.
Pierce at least 10 enemies with a single cannonball.
Obtain the Water Element.
Kill 200 Enemies with the Thompson Submachine gun.
Kill 250 Enemies with a shotgun.
Kill 150 Enemies with the Rocket Launcher.
Obtain the Fire Element.
Obtain the Earth Element.
Obtain the Air Element.
Complete any level in co-op.
Complete a level in co-op with blood option set to hippy.
Frag a total of 100 players.
Win a versus match.