Here is the full list of all 54 Serious Sam 4 achievements. It takes around 15-20 hours to unlock all of the achievements on Windows.
Make 20 enemies kill each other using Psychotropic Grenades.
Meet a powerful granny.
Assist Dr. Vermetti in his war on worms.
Make sure Gabriella is OK.
Party like it's 199.
Kill 20 enemies while dual wielding double shotguns.
Sign Secchi's rifle.
Head into Rome. Ditch Rodriguez.
Get a weaponized black hole, using science.
Kill 5 enemies in a row while your health is below 10 HP.
Run away from an angry volcano you foolishly antagonized.
Collect scorched aliens for Professor Kiesel.
Die HAARP With A Vengeance.
Kill an Aludran Reptiloid using nothing but a pistol.
Kill 5 enemies during a single Time Warp slowdown.
Recover the alien artifact located by Dr. Stein.
Find out what happened to Alessandro.
Recover a key stolen by a cultist.
Get together with your friends and kill something big.
Fight alongside Massimo Murena.
Unlock a S.A.M.
Save the rookie. Find Father Mikhail. See the sights.
Kill 3 enemies with a double shotgun blast.
Get knocked on the head and remember how you got here.
Ride the Popemobile to victory.
Don't fear the reaper. Be the reaper.
Cross the French countryside and get very cross.
What if you could talk to the monsters?
Navigate the citadel of Carcassonne. Start reassembling your team.
Get justice. Get the Holy Grail. Get screwed over.
Escape the Oil Rig.
Send Mental a message he won't forget.
Beat the game on any difficulty.
Unlock 10 S.A.M.s in a single playthrough.
Destroy 10 propaganda drones.
One-shot kill 3 Werebulls with a shotgun.
Melee a big enemy.
Use the mininuke to eliminate 100 enemies at once.
Kill 100 enemies with a headshot.
Kill a Belcher using Belcher collateral barf damage.
Kill 11 different enemies using melee attacks.
Kill 50 healthy Kleers with a direct double shotgun hit.
Spend 1000 minigun rounds while firing continuously.
Harvest 100 enemies with a combine harvester.
Kill a Witchbride using C4.
Dismember 50 enemies with cannonballs.
Find out what happened to the English airman.
Assist a couple of young ladies out hunting.
Discover Fulbert's great invention.
Protect humanity's treasures from invaders with no taste.
Achievement is your middle name.
Save a princess. Doesn't get more classic than that.
Go on a date with Hellfire.
Finish a text adventure. On an oil rig. During an alien invasion.