A master of a single weapon.
Think Gimli with his axe.
Level 3
Favored Weapon.
Choose a favored weapon (Longsword, Longbow, etc.). When attacking with that weapon, deal +10 damage vs. Armored Foes.
Level 7
Muscle Memory.
You have advantage on your first attack each turn when using your favored weapon.
Level 11
Deadly Expert.
When you use Bloody and Dangerous while wielding your favored weapon, roll 1 extra Hit Die for free (you must still spend at least 1 of your own).
Level 15
Practiced Strike.
(1/Encounter) When you use Bloody and Dangerous while wielding your favored weapon, you may use the maximum value for each die instead of rolling.