Here is the full list of all 19 Sea Salt achievements.
Defeat Admiral Pierce
Complete the Story
Beat all Arenas
Clear every level
beat the game on Hard
Beat one Arena
Unlock all Apostles
Collect all Cards
Kill 666 enemies
Kill the devs
Unlock the Hunter Apostle
Spare the Witch
Defeat Wharfmaster Glenn
Defeat Deacon Raphael and his Mob
Defeat the Lone Warden
Defeat the Thistle Guards
Defeat the Witch
Defeat Count Volgrave
Defeat the Archbishop