*UPDATE*
After reading Flowerx's post http://forums.spiralknights.com/en/node/57841 I thought of a new weapon, the Leech Fang. This sword goes from 3-5 stars and drains about half a block of an enemy's health. The Leech Fang is a black katana with a dark red-colored handle, looking alot like the Archeron http://wiki.spiralknights.com/Acheron, but with parts of the blade sticking out at the end like two fangs, with the fangs growing in size as you progress through the alchemy path. It also has a red aura surrounding it.
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First alchemy path:
3* Leech Fang
4*Vampiric Leech Fang
5*Drain Edge

Second alchemy path:
3* Leech Fang
4* Burning Leech Fang
5* Hell Fang
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Damage:
The Leech Fang is the first sword to do two types of damages, mainly shadow and medium piercing, because of that, however, it's damage is decreased slightly. It also has a slight chance of doing poison.

Basic attack:
The Leech Fang's basic attack is, first two basic slashs draining no health, then two stabs, one tearing through the enemy lunging forward the other ripping out backward. The stabs do two hits each draining the enemy of some health and giving it to you. As a means of keeping you from draining tons of health from enemies, the weapon needs a small charge by not attacking at all for 1 min in order to drain health with its stab attack.

Charge attack:
The Leech Fang's 5 star charge attack is a forward jab, sending a dark-red hologram of a greaver http://wiki.spiralknights.com/Greaver flying straight forward for 2.3 seconds, draining health from all enemies it hits. Its 3-4 star charge attack is a basic 5 hit combo draining energy with every-other hit. The charge attacks increase the charge time of the Leech Fang by 2 mins.

The Hell Fang's charge attack is the same as the Drain edge except with an orange hologram of a ruby greaver. The Hell Fang has a good chance of doing fire.

*If you have any spare time I would really like a drawing of this sword's alchemy paths.*

*UPDATE*
You now have to stand completely still for the Leech Fang's drain to charge back up, its charge is represented by the red aura surrounding it. If the red aura is not present you can't drain energy with its stab or charge attack.