The arms master is all about trading the ability to hit for more opportunities to strike and more damage. Of course, you will need more than one knife to do the job. If you find your self hoarding weapons you don't seem to use, well them maybe think about becoming an arms master, wielder of all the weapons.

Combo

When you choose this archetype at the 3rd level, you learn how to maneuver each attack you make into exceedingly more elaborate swings and cuts. Once per round when you land a hit on a creature you gain a stack of Combo. For every stack of Combo you have you take a -1 penalty to your attack rolls. If an attack hits, and you have any Combo stacks you add and additional +2 to the attack's damage for each Combo stack you have. Combo stacks last one minute or until you miss on an attack roll, and then they reset to zero. You can not have more combo stacks than your fighter level.

Chain

At the 7th level, you become adept at drawing weapons and attacking swiftly in one action. You Stow a multitude of different weapons on your person. Having these weapons readily available allows you to make additional attacks during your attack action by dropping a weapon in your hand. During your attack action, you may drop a weapon and make an attack roll with another stowed weapon. Weapons dropped this way take an action to retrieve.

You can Chain as many times as you have a Stowed weapon available. If you have only one weapon on you, you can not continue the chain. You may Stow a number of additional weapons equal to one third your fighter level. You cannot stow more than one weapon with the Heavy feature.

Finisher

Starting at 10th level, when you land a decisive blow to your foe you can choose to end a combo early for increased damage. When you land a critical hit you may choose to reset your combo stacks to zero to add an additional +2 to the attack's damage for each Combo stack you had.

Combat Retrieval

At 15th level, you can retrieve a weapon dropped by your Chain feature as a bonus action. Additionally, on your turn, when you reduce a creature to 0 hit points with a melee weapon you can retrieve one weapon within 5 feet of you without spending an action or bonus action.

Quick Combo

When you reach 18th level, once per long rest you spend a moment of combat to visualize your next combo on a creature. You may use a bonus action to gain nine Combo stacks.