Regarding ...h5 in the Smyslov, the game I most readily recall is Augustin-Nunn, but I also seem to recall the exchange sac on h4 happening back in those days (1977ish).

There was some analysis on this in NIC some months ago, but it seemed to agree with the old view that White might as well play 6. Nc3 d4 7. Bg2.  I don't see how Black has "skipped through a lot of other alternatives which the White player might have had in the meantime."

While I was lurking around the deepest darkest depths of 4 knights theory just tonight I stumbled across this little curiosity, and remembered reading about it.

1. e4 e5 2.Nf3 Nc6 3.Nc3 Nf6 4. g3 Nxe4?!

A Reversed Halloween Gambit! A little 2-liner on the wiki page for the normal Halloween says: 

"A similar gambit can be tried by Black: after 4.g3, Black can play 4...Nxe4!? This line is arguably sounder than its White counterpart because White's 4.g3 has weakened his f3-square. Moreover, White cannot play the line recommended by Kaufman with colors reversed, because 5.Nxe4 d5 6.Nc3 d4 7.Bb5? dxc3 8.Nxe5? Qd5 9.Qe2? loses to 9...Qxh1+. However, with the pawn on g3, Nh4 is possible and it should be easier to castle."

Sadly the source for that quote is a website called Chessville which has suffered a sad death since then. I can't see Nh4 being of particular use to white, unless you're wanting to offer black another target for tempo-gain one day, so I wanted to look up the justification for this Nh4 idea. Website=gone, though.

I also found some other blog post (8 years old) which had a link to some analysis but that link was defunct, too. 

Anyway, I thought a nice little source of info for those looking for it could come from us friendly folks on here. I personally have never played the Halloween (with either colour!?) so I don't know a huge amount about it. 

What I do know is that the two mainlines for black in the regular Halloween are not possible this way around, one being the line:

1. e4 e5 2. Nf3 Nc6 3. Nc3 Nf6 4. Nxe5 Nxe5 5. d4 Ng6!
Here Black tries to hold the piece, but obviously in our reversed version there's a pawn there. 

The other being the following: 

1. e4 e5 2. Nf3 Nc6 3. Nc3 Nf6 4. Nxe5 Nxe5 5. d4 Nc6 6. d5 Bb4! 7. dxc6 Nxe4 8. Qd4 Qe7.

However, if you play exactly those same moves out with colours reversed and g3 being inserted, you will find a rook hanging on h1. Therefore this line doesn't work either. 

I know that an option for white is to give the game up and transpose back into a mainline Glek (which he probably wanted):

1. e4 e5 2. Nf3 Nc6 3. Nc3 Nf6 4. g3 Nxe4 5. Nxe4 d5 6. Nc3 d4 7. Bg2 dxc3 8. bxc3 

And we have a Glek (a magical move later than it should be!) but generally speaking it's safe as houses for Black anyway, and we've skipped through a lot of other alternatives which the White played might have had in the meantime. Admittedly we've done some other learning to bridge the gap, but I'd take learning Reversed Halloween over Glek anyday!!

I've dug up a game which doesn't appear to be on chessgames.com as a sweet example of when things go right:

1. e4 e5 2. Nf3 Nc6 3. Nc3 Nf6 4. g3 Nxe4 5. Nxe4 d5 6. Nc3 d4 7. Nb1 [7. Nb5 a6 8. Na3 e4 9. Ng1 also gives Black promising compensation for the piece, for instance 9... Qf6 prepares to attack f2 with ... d3 and ...Bc5.] 7... e4 8. Ng1 This is how most people play the position. [8. Nh4 is the computer's recommendation, but Black keeps good compensation with 8... Qe7 followed by ideas of ...d3 or ...Ne5/...g5/...Nf3.] 8... d3! This pawn proves again to be a major bone in White's throat, which threatens to choke him if he cannot get his king out of the centre. 9. c3 Bc5 10. Qh5 Qe7 11. Bh3 g6 12. Qh6 f5 It's hard to dispute Black's advantage - White can hardly move a piece! [12... Ne5! may have been even better, intending to jump into f3 if permitted.] 13. b4 Bb6 14. Bb2 Be6 15. Na3 Rf8 White has tried to play around Black's beautiful pawn chain from h7 to d3 but his position still fails to make sense. 16. O-O-O? Funnily enough, the king was safer in the centre. 16... Bxa2 17. Rf1 O-O-O 18. Bg2 a5 Once White's king is opened up, he's toast. 19. b5 Ne5 20. Nh3 Bc5 21. Nb1 Qf7 White resigned as he can't prevent ...Qb3-c2 mate and 22. Kd1 Qb3 23. Ke1 Qxb2 gives Black the unstoppable threat of ...Qc1 mate.