OOC: It's provably 0. You can definitely use it in, say, a grapple, where you are known to be touching your opponent (assume the case of a visible opponent). The only question then what is required when you cannot see your opponent? Touch--however that is resolved.
The second question, however, is whether you want to back up the combat one round to allow Uri the same action. (And then I don't think Offal will do it, too, if her invisibility is knocked out.)