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