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