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