An Arma Dominus is a master of many weapons, but there is one weapon that they will always prefer. Whether it's a dagger that they were given by a mentor, a bow that belonged to a parent that was killed by a great beast, or a weapon that they received as a child that helped them survive in a harsh world, that weapon will be one that they will be better with in fights and they will know how to use that weapon to do many masterful things.

Arma Dominum

When you choose this subclass at 3rd level, there is one weapon that you have great skill with, a non-magical weapon, that you choose. When you make an attack with your chosen weapon, when you roll a 19 or 20 on a d20, the attack is a critical hit. Also, when you roll for damage on a critical hit, the damage is the maximum amount for that attack.

Arma Armorum

Starting at 7th level, you can use your reaction to add your proficiency bonus to your AC when you are attacked. You can use this ability once per long rest. When you reach certain levels in this class, the number of times you can use this increases. Twice at 10th level, three times at 15th level, four times at 18th level.

Arma Virtutis

At 10th level, your chosen weapon counts as a +3 magic weapon.

Arma Perfectum

Starting at 15th level, your weapon attacks with your chosen weapon score a critical hit on a roll of 18–20. Also, when you roll for damage with your chosen weapon, the amount of dice you roll is doubled. (Example: 1d8 becomes 2d8, 2d6 becomes 4d6).

Arma Mortis

At 18th level, your chosen weapon becomes sentient with INT 14 WIS 14 CHA 14, the same alignment as you, the ability to speak one language that you can of your choice, and the ability to cast one cantrip of your choice at will from the following list:

Acid Splash

Chill Touch

Control Flames

Create Bonfire

Dancing Lights

Druidcraft

Eldritch Blast

Fire Bolt

Frostbite

Guidance

Gust

Light

Minor Illusion

Poison Spray

Produce Flame

Ray of Frost

Sacred Flame

Shocking Grasp

Spare the Dying

Thunderclap

True Strike

Vicious Mockery