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