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