The Cozio Defense is started by the perhaps surprising move 3...Nge7. Black temporarily hems in his dark square Bishop. But then you have the option to fianchetto the Bishop or ...Ng6 is sometimes played.
You have three main options with the White pieces. You can castle and take command of the central files. You can build a big center with 4.c3. Or you can develop with 4.Nc3 and see what Black has in mind before committing to a plan.
As Black your main decision is centered around your approach to the middlegame. You can play positionally by fianchettoing the Bishop and slowly gaining equality. Or you can play ...Ng6 and ...d5, going for piece activity and earlier pressure against the White King.
Vasily Smyslov was a positional player at heart. Like all of the greatest players he could spot a tactic as quick as anyone, and play it if it made sense. He did not seek out that type of game though. He was like I'm going to play 40 good moves. If you play 40 good moves we will draw.
He wasn't going to be reckless and gamble with razor sharp, deep tactical play. He was going to simply play great chess. If you could not play at his level he was going to punish every slight inaccuracy. Very few could play at his level.
You can rest assured all of his contributions to chess theory are going to be positional in nature. Playing for small advantages. Sometimes abstract elements to the untrained eye. Smyslov knew how to nurture them and make them grow.
His move here 3...g6 preps the Bishop for the long diagonal and concedes no structural weaknesses. He answered 4.c3 with 4...a6 putting the question to White's light square Bishop. If you face this system with White, try instead the immediate 4.d4 exd4 5.Bg5 and see if you can make anything of the resulting pressure. Remember you're playing against the Smyslov Defense, not Smyslov!
The main idea of Bird's Defense is to limit White's space. You are playing 3...Nd4 to fork and provoke a Knight trade. It's practically forced if White wants to keep his light square Bishop in the game.
After the trade you as Black are occupying d4 with your pawn. You prevent White from playing d4 himself at some point. This is a move that he would usually like to play sooner or later. Solidify this pawn with it's control over c3 and e3 and White will not be pleased.
You're White, and you have to do something. Great, you can't expand on the Queenside so castle Kingside and surge forward with f4. With no e-pawn to check your e and f-pawns, Black's going to have to concentrate his energies on blocking this diabolical duo.
The Steinitz Defense secures Black's e-pawn and the light square Bishop is coming to d7 next move to relieve the pin. Black's structure is solid and he can develop with ease.
But you might have one bone to pick with the Steinitz. It's the move 4.d4 which is potentially troublesome. Remember you're not putting any difficult questions to White yet in terms of his development. You're allowing him to develop without hindrance.
So if he can play d4 and recapture to attack the pinned Knight with his then he is sort of gaining the initiative. It's not like White is winning material or inflicting positional concessions on you. It's just that he's got this annoying pressure on your position.
A lot of people throw in 3...a6 4.Ba4 to make it a Neo-Steinitz. Then after 4...d6, 5.d4 doesn't work as Black can now break the pin with ...b5. That's not to say that the regular Steinitz isn't perfectly playable. You just need to be accurate that's all.
This move is also known as the Jaenisch Gambit and it is as much fun as it looks. It has shades of a King's Gambit or maybe Vienna Gambit with the White pieces.
It probably can be refuted with the right moves but it must have an unsettling effect on many amateurs. Let's face it, you play the Ruy Lopez, you're not thinking about dealing with this challenge to your e-pawn on move four.
Don't be too eager to accept the gambit if you haven't studied the lines. The pawn push ...e4 can cause pandemonium in the White camp. In some games Black has been able to get his central pawns rolling en mass, crushing everything in it's path. Probably 4.Nc3 or 4.d3, supporting the pawn is the safest option for the uninitiated.
The Cordel Variation which you might know as the Classical Defense was one of the main answers to the Ruy Lopez once upon a time. Along with 3...Nf6 (the Berlin Defense) this was a standard reply before Morphy started playing 3...a6.
Play this as Black and you have two ways to interpret the opening. White will either castle or play c3 to prepare d4. If you see 4.c3 and you want a crazy game, you can play the Cordel Gambit 4...f5.
If you don't like so much bloodletting you can play the much more sober 4...Nf6. In the case of 4.0-0 this is the better option. You're set up for a positionally orientated game.
As White this is okay. You will have a little more space and a small lead in development. Your position is solid but you'll need to play well to win.
The Berlin Defense, 3...Nf6, has always been around. When the first great international tournament, London 1851 was held, it would have been top of the list to answer 3.Bb5. Then it fell away a little.
It never completely disappeared as it is a great choice for Black against the Spanish. It made a huge comeback in 2000 when Vladimir Kramnik used it to beat Garry Kasparov in the World Championship. Now every top player plays it regularly.
The great thing about the Berlin is Black can give himself winning chances and keep his position solid. Sounds like he having his cake and eating it. An early Queen trade blunts White's attacking edge.
Black loses the right to castle but with the Queens off and White's a-Rook ages from being developed it scarcely matters. White can still play for a win but with Black's counter play, it really is a 50/50 game.
So the Morphy way is not the only way to play. Both sides can choose in positions rich with offensive and defensive resources. Black can hang in there and work his way into the game or he can attack from the first bell.