Baron Sablemane's Poison is a special concoction made by the Baron for Rexxar.
You will need:
Here, take this to your master. I'm sure that whatever the reason, Rexxar will put it to good use.
Oh, and do be certain to remind him that he owes me.
He knows what I want, and I'm certain that however he intends to obtain it for me, I'll be seeing you again sooner than you think.
Now, do be a good little <boy/girl> and run this up to Rexxar.
<class>, you are back so soon? Do you have the poison?
This is unsavory business, this use of poisons. But it will do what we want.