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