Thanks to Karla for an enjoyable and novel endgame.
As per usual I'm left with one unparsed clue...
23d - Energy Nick finally increased 20-fold (5)
I've been working on the assumption that "Nick finally" is a Roman numeral but, even if that's the case (which I'm now seriously doubting), I don't see how multiplying it by anything gives the answer, unless it = F which you then a synonym of?