In my experience, I have found that it is never unuseful to have a quick, offensive weapon handy to me at all times. In earlier times, I had to make do with the helpful, but somewhat limited, ability of my 'Arms of the Abyss' when no other tool was readily available for my offensive or defensive needs.
However, practice and trial-and-error have resulted in what, I believe, is the Zenith of what a simple shadow can be made to do in such a capacity. With this technique, it is now possible to create 'Arms' with a razor edge, that still retain the benefits of the standard Arms, but now can inflict immediate damage upon a target when required to.
I had always wanted a Ventrue pin-cushion. Ah, and there she is... stuck to my wall.
-Nilijandro Lara

Tabletop System:

When achieving the required levels of the two disciplines, the player can spend 24 experience points to acquire this added ability.

When enacted, the characters Arms of the Abyss now have the option of being imbued with the same qualities of a standard slashing weapon.

After the initial Manipulation + Occult roll to create the arms, an attempt to strike with the 'Spike' requires at least one success on an additional Manipulation + Occult roll to hit. A whipping 'Spike' now inflicts the same amount of damage as your standard 'Sword' (Strength +2), on a successful hit. Otherwise, there is no change to the Arms themselves, their capabilities, or weaknesses.

Minds Eye Theatre Rules:

Upon achieving the required levels of the two disciplines, the player can spend 9 experience points to gain this power.

Once bought, 'Shadow Spike' allows a players Arms of the Abyss to inflict 2 levels of lethal damage on a successful Physical challenge, when using an Arm against a target. The spike's damage level may be increased by one level of lethal damage, should the character imbue the Arm(s) with 5 levels of Potence. All other rules for 'Arms' remain the same.