Exsanguination is a Blood-typed offensive move.
It's one of the only Blood moves that requires contact with the victim.
The coils around the Spearow's body start to tighten, and for an instant it looks like he's threatening to crush the pokémon using WRAP, before it becomes clear that it's not that lucky. The thin, sundew-like stalks grow rigid and sharp, piercing into the Spearow's flesh, eliciting a strangled cry from it. The tendrils begin to glow with a dim red light as they suck up the pokémon's blood, and Saccharine utters a soft purr as he feels the Spearow's life flooding into him.
Mercifully, the Spearow loses consciousness a few seconds into the process, but it continues on even after it's fallen, tendrils coiling tighter to sap up every drop of blood they can get. It's almost a full minute later that Saccharine finally drops the lifeless husk, swollen tendrils unwinding from it with a certain giddy energy that he can't quite seem to shake. He turns his crimson eyes up to Devi, cooing softly. Did he do a good job?
~Reshigah, Togi, 2012-11-25 session
As you can see, it has rather vampiric qualities.
It's a move that cannot be learnt by non-Blood pokémon - less due to the mechanics and more because consuming large quantities of blood makes non-Blood pokémon rather ill. For Blood pokémon, however, it has the qualities of a stimulant drug, easily (but not always) to point of euphoria. It's that effect that makes the move dangerous to use, as occasionally, a pokémon using it simply will not stop until the creature it's feeding off of is dead.
It has a rather low accuracy in battle situations because of the kind of delicate contact it requires - although, starting is not so much the problem as actually getting anywhere substantial with it. On immobile targets, it's of course not a problem, though, so a victim that's WRAPped or paralysed will have a much harder time fending it off.