Here is the full list of all 10 Hail to the King: Deathbat achievements.
You beat the game in Nightmare Mode without losing a life!
You beat the game without losing a life!
You talked to all the NPCs!
You beat the game in Nightmare Mode!
You acquired every weapon in the game!
You beat the game!
You acquired all of the lost art!
You opened all the bonus levels!
You completed the tutorial!
You talked to an NPC!