This is not a spell, but rather the effect of casting Vampiric Embrace on yourself. [b]
[b]Vamiric Embrace is a 8th level Necromancer spell & a 22nd level Shadowknight spell.
Click HERE for more details.
Esentially, Vampiric Embrace places a short lived buff on you.
This buff (VampEmbraceShadow) will give you a chance to drain your opponents hit points while engaged in melee combat.
The buff is scaled to your level, meaning the spell will grow in power as you grow in levels (e.g. more hit points drained, longer duration).
The VampEmbraceShadow effect can also be obtained through Alternate Advancement or certain items that have this effect built into them.