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