I have an idea for how to make a dagger that can work like a sneak attack dagger without actually having it check to see if you at the enemies back. Rather than attacking the back, which sometimes is impossible as enemies spin at sonic speeds, the weapon simply charges up for a single attack with super high damage. The part of the weapon that makes it a sneak attack is that it will drop the charge if you are attacked, similar to rejuvenation. This way you have to sneak the attack in as to not be interrupted.