Here is the full list of all 16 Howl achievements.
Unlock the last scroll slot.
Set fire to three enemies with a single Exploding Shot.
Gain all Confidence.
Gain every Skull.
Defeat the origin beast.
Kill three enemies with a single Piercing Shot.
Unlock level three for all skills.
Kill two enemies with a single Vault.
Defeat the white beast.
Enter the Cathedral.
Kill an enemy while under the effects of Shadow Step.
Use three skills in a single round.
Kill two enemies with a single Smokebomb.
Defeat the pack leader.
Unlock level three for any skill.
Kill two enemies using Force.