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