Mastery Property. Your training with weapons allows you to use the mastery property of two kinds of Simple or Martial weapon of your choice, provided you have proficiency with it. Whenever you finish a Long Rest, you can change the kind of weapon to another eligible kind.

When you reach certain Blood Hunter levels, you gain the ability to use the mastery properties of more kinds of weapons. Improved to 3 mastery at level 4, and 4 mastery at level 10.