What's the exact difference between (-)-BTX and (+)-BTX I quite liked this article, which describes the synthesis of (-)-batrachotoxin as well as a steroisomer, (+)-batrachotoxin. I would like to know what the precise difference is between the two: are they precise mirror images of each other, or is there something more subtle going on? Is there something specific about the (±) notation (as opposed to S and R, for example) with relevance to the difference between the two?

I had a look online but the original paper is thin on structures that I can understand, and just going on google buries me under a slew of (-)-BTX results.
From a cursory glance, batrachotoxin has 8 stereocenters. No single Cahn-Ingold-Prelog R or S designation is going to be enough. As a result, we simply identify which enantiomer we're talking about by using the standard optical rotation of the substance. The (+) and (-) forms are enantiomers. They rotate plane polarized light in equal and opposite directions and are non-superimposable mirror images of each other.