Well, there are basically 2 ways to do the tesla:
1. simply make it a like a mundane taser gun, nothing fancy about it. Targeted with weapons, deals stress equal to the number of shifts of the attack and places "electrocuted" on the target
2. make it an Item of power with breath weapon (lightning)
which you take depends whether or not you think it should cost refresh to wield a weapon like that.
The goo does not need any stats, I think. It is simply a plot device used to neutralize the artefacts. Some artefacts might need more than simply the goo, like The Spray paint, that needed to be neutralized by reversing the destructive symbolism, after it was covered with the goo
.
There was another thread about that somewhere, not long ago, let me see...
Here it is:
http://www.jimbutcheronline.com/bb/index.php/topic,28770.0.html
Damn, Sanctaphrax was faster.