Here is the full list of all 37 Hunt: Showdown achievements. It takes around 200 hours to unlock all of the achievements on Windows.
Kill 100 enemy Hunters with headshots
Recruit 100 Hunters
Complete 100 Bounty Hunt contracts
Investigate 250 clues
Retire 25 Hunters
Kill 50 contract targets solo
Close 250 rifts in Quickplay matches
Have 5 level 50 Hunters at the same time
Break 50 doors
Burn 50 chicken coops
Kill an enemy Hunter with a sledgehammer throw
Complete a weekly challenge
Unlock 25 entries in the Book of Monsters
Unlock Bloodline rank 100
Play the gramophone and the piano in one mission
Locate a contract target without investigating a clue
Hide in a toilet
Visit every Lawson Delta location in one mission
Visit every Stillwater Bayou location in one mission
Be on fire, poisoned, and bleeding at the same time
Kill 150 Grunts with the dusters
Have 15 traits on a Hunter at the same time
Unlock Bloodline Tier 3
Unlock 50 entries in the Book of Weapons
Unlock Bloodline Tier 2
Get a Hunter to level 50
Complete a daily challenge
Kill 150 monsters with headshots
Complete your first Bounty Hunt contract
Complete Trainee Mode
Kill any contract target with a melee attack
Kill an Immolator without making them explode
Kill your first enemy Hunter
Absorb at least 250 energy from the Wellspring in a Quickplay match
Survive a Quickplay match
Be the first to activate the Wellspring in a Quickplay match
Be the last Hunter standing in a Quickplay match