Double targeting is currently not allowed.
Well, there you go.
Thematically, I would suggest this:
: Target a creature. Rob it of one attack or one defense.
The ATK/DEF would be chosen by which is higher on the targeted creature. You gain one of that stat.
I would also suggest that you lower the attack to 0 | 1 starting out, but keep the defense level. This makes it more balanced.
If anyone argues OP, either raise the ability cost to
or lower the defense by one.
Nice avatar as well.
Editing my previous post to reflect the new element suggestions. It could be Life, guys! Leeches are alive and found in nature! Admittedly Water would be a good combo, but still.
As for poison, I don't think it really needs to do much. Yes, leeches are bad, but do they poison you?
I think the leeches suck poison OUT not put it in... at least thats what I'm reading out of it so far.
Draining att / def and sucking out poison counters seems to fit leeches pretty well to me.
I could see the card fitting either

and

or

and

too... but the whole sucking the life out of things seems to link better with

or

than

. Plus we already have a

and

synnergy card (forest spirit).