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