Besides being the only black reward card at the moment... anything that automatically drains enemy HP in my books is definitely something worth investigating.
P.S. Any idea where we can read up on what the new abilities actually do? i.e. Does "life leech" drain 1 HP from every monster every round, or 1 monster every round, or all monsters just once at the start of the round?
For the vampire above it needs to strike and remove a heart from an enemy to gain one itself.
You might be interested in the below link. It has some info abilities. I am not sure if the new cards are added to the info provided below or not.
http://steemmonsters.wikia.com/wiki/Abilities
hmmm... that's pretty cool (would have been epic if it auto-drained one from enemies every round though :P)
P.S. Where did you find out about this ability (have you played with it and saw it happen)... that link doesn't have the new ones on it yet.
I played vs. in battle.