The Mongolian Attack

The Mongolian Attack is a lesser-known and lesser-played opening characterized by white playing Nd4 after Nf3.

While some may consider it to be a Common Opening, it is slightly too obscure to hold that title.

The opening is named such because of the nature of the attack, it features white moving his kingside knight into the attack, and in some lines, may be white's only developed piece for up to and including 4 turns.

This is different from the mainline in the way that instead of pushing a pawn to d4, white places a knight instead, meaning that the king's queenside trigonal is never opened, allowing for white to play a different developing move as opposed to blocking the trigonal with c3 on move 3.

However, one of the weaknesses of the Mongolian Attack is that the f-file's diagonal is immediately opened up by white, as opposed to the mainline where the knight will stay on f3, keeping the file blocked and the f pawn protected, however white is able to play 3. e3 4. Qf3 to re-protect his f-file from future attacks.

Replies
There are multiple replies to the Mongolian attack, they are listed below.

After 2. ...c5, Sicily Defense
Another weakness of this opening is the fact that white's knight is now somewhat misplaced on the 4th rank, allowing black to push his e or c pawn to attack white's misplaced knight, pushing the e-pawn 2 forward is generally considered a bad move as it permanently weakens the squares directly in front of the king, allowing for future diagonal attacks, making it not a viable continuation of the defense, however black can place 2. c5, attacking the knight and opening up the queen simultaneously, after the knight is kicked, white has 4 good squares to move the knight to, f3, f5, b3, and b5, moving the knight to the b-file is quite inactive and most attacks that white might have on that side of the board may be defended with 3. ...Qb6, which was the move black wanted to play all along, as it is the secondary purpose of 2. ...c5.

White does have the option to play 3. Nf5 (Triple Variation), threatening to play 4. Nd6+ opening the e-file because black's only response is to play exd6, revealing the black kings diagonal, a response to 3. Nf5 is g6, attacking the knight, however this does not defend against Nd6+, and is considered a bad move, an alternative is e6 opening up black's dark square bishop, protecting the d6 square from the knight, this also attacks the knight, on f5, however capturing is considered a bad move because it would open up the e-file for the black king, this line (1. Nf3 Nf6 2. Nd4 c5 3. Nf5 g6 4. Nd6+ exd6) is named the "Four Horsemen Variation", named so due to white having played 4 knight moves in the opening.

White earns a tempo at the end of this line, as Black will seek to kick the White knight from f5 by playing 4. ...g6 after white makes next move, if white chooses, they have the option to perform a turn 2. f7 sacrifice as black may be too hung up on taking the knight, this turn 2 sac is not a mating sequence, and any moves beyond 4. c3 g6 5. Qb3 gxf5 is considered out of the opening, black has the option to prevent the turn 2 sac by playing 4. ...c4, attacking the b3 square, preventing the white queen from moving there and performing the sac, there also exists 4. ...Qb6, and after 5. Qb3 black will play 5. ...Qxb3, trading the queens off of the board, beyond this point is considered to be out of the opening.

Another option after 2. ...c5, is to play 3. c3, opening up the queen and threatening a turn 1 f7 sacrifice, black can counteract this with either 3. ...c4, or 3. ...Qb6, both attack the square the white queen wants to go to, and successfully defend against the f7 sacrifice, after 3. ...c4 we are out of the opening and the line is called The Advance Variation, the alternative, 3. ...Qb6, is called The 43rd Variation.

After 2. ...d5, Mainline Defense
Black may attempt to play the Mainline Defense against this opening, continuing with 2. ...d5, seeking to play 3. ...c6 next, finishing the mainline defense, as the Mongolian attack defends f7 after 2 moves and the mainline defends after 3 moves, White gains a tempo from black attempting to reply with the mainline defense, White could play 3. e3 with plans to develop the Queen using the tempo earned from the fact that black must play c6 to finish his mainline defense, Qf3 is considered to be out of the opening (specifically 1. Nf3 Nf6 2. Nd4 d5 3. e3 c6 4. Qf3) (Mainline Defense: Success)

Instead of 4. Qf3, white has the option of playing 4. Nb5, and after 4. ...cxb5 white can recapture with the newly opened bishop on f1 with 5. Bxb5+, at which point black has 4 options to block the check, as moving his king is not possible, these options are 5. ...Nc6, 5. ...Nd7, 5. ...Bd7, and 5. ...Qd7, Qd7 is considered a blunder as it loses to 6. Bxd7, winning a Queen for a Bishop, Black may seek to play Nd7, hoping for 6. Bxd7 Qxd7, trading a knight for a bishop and developing the queen, however white does not have to trade the knight for the bishop and may instead leave the bishop on b5, absolute pinning the black knight to the king, this is considered bad for black as it chokes in his light-squared bishop, but black does have the option of playing 6. ...a6, attacking the Bishop, then 7. Ba4, followed by 7. ...b5 (the unpinning line), attacking the bishop and unpinning the knight, however, this line does come after white plays his 6th move, White could play 6. c3, thus if black plays 6. ...a6 the a pawn will be pinned to the rook on a8 after 7. Qa4, effectively neutralizing black's attack on the bishop, black might be able to capture the bishop in spite of the pawn being pinned, trading a rook for a bishop and a knight, which is generally considered good for the player who is down the rook, as bishops and knights are worth more than rooks by general consensus, after 7. ...axb5 8. Qxa8 this is considered to be out of the opening.

White can also attempt to gambit his C pawn in an attempt to delay black's 3. ...c6 with 3. c4, attacking black's d-pawn, black could choose to ignore this attack and play 3. ...c6, allowing white to play 4. cxd5, after which, black must capture with the knight or the queen, as capturing with the c pawn would permanently weaken the black king's queenside tri/diagonal.

After black recaptures the pawn on d5 with the queen (4. ...Qxd5), white's knight will be under attack, white has the option to play 5. e3, defending the knight from the queen, black does, however, have the option to capture the knight despite e3 being playing, as if white wants to recapture the queen they would need to open their e-file with exd5, permanently weakening the white king's e-file diagonal, this may be seen as a fair trade as black will be down a queen after exd5, players can perform this opening at their own discretion.

An alternate defense of the knight is found with the move 5. Qa4, preventing black from taking the knight, as now they would no longer open up the e-file, lines exist where black plays 5. b5 attacking the queen, but these lines have yet to be explored thoroughly, so as of 5. Qa5, we are considered to be out of the opening.

After 2. ...Nd5, Symmetrical Variation
Both players have defended against the Turn 0/1 f7 sac beyond this point, but as white is up a tempo is this position, they he is considered better.

White may seek to solidify his position with 3. e3, or continue on the attack with 3. Nf5, both moves are able to be mirrored by black, if 3. e3 e6 White will have the option to play 4. Nf5 in an attempt to get Black to take the knight and open his e-file, black can always continue copying white with 4. ...Nf4, but this is considered bad as white will have the opportunity to play 5. Qf3, attacking the knight, after black moves his knight away with 5. ...Nd5 white is considered better as they are up on development and a tempo, if black is still insisting on copying White some more, they can play 5. ...Qf6, which instantly loses a knight to 6. Qxf4, which protects white's own knight in the process of capturing.

After 2. ...Nc6, Black Mustang Defense
Black seeks to trade his knight on c6 for the knight on d4, but this blocks his c-pawn for long enough to make him unable to play a T0 F7 sacrifice, white has multiple options from this point.

White can trade on c6, with 3. Nxc6, but this is generally considered a bad move as after bxc6/dxc6 white will be down on development, this trade is called the "Black Mustang Accepted", and after which, we will be out of the opening.

White could choose to move his knight away, like in the Sicily Defense, there are multiple squares for the white knight at this point, b3, b5, f3, and f5, unlike in the Sicily, moving the knight to the b-file isn't such a bad option, as black can't instantly move his queen out to attack the b-file, these moves are quite inactive, and both result in the Black Mustang Declined variation, after which we are considered to be out of the opening.

The f-file looks like a better place for the white knight, White could play Nf5, which doesn't threaten the same things as in the triple variation of the Sicily as black still has his c pawn on c7, where it is able to capture on d6, preventing the entire idea, the line leading up to Nf5 (1. Nf3 Nf6 2. Nd4 Nc6 3. Nf5) is named the triple variation of the black mustang defense, from here, black has the option to further harass the white knight with g6, the white knight does not have many squares to go to from f5, Ng3 is, at a glance the best continuation of this line, as it doesn't block in the e pawn, allowing for the queen to come out to f3 sooner or later, another option is Nh4, which allows the knight to rotate back to f3 on the next turn, black is considered better in this line.

Another response to the Black Mustang is of course pushing a pawn to the 3rd rank, defending the knight, the e-pawn is a no-go for obvious reasons, however the c pawn is clearly the better option, the line (1. Nf3 Nf6 2. Nd4 Nc6 3. c3) is named The White Mustang, and after Nxd4 4. cxd4, it is The White Mustang Accepted, as white can immediately get his queen out following the trade, he is considered better, and has the option of a turn 2 sacrifice following the trade.

Any move that does not defend the knight is referred to as the "Black Mustang Gambit Variation", and is considered worse for white, after which, we are out of the opening.

After 2. ...e6, France Defense
This is considered a sound reply to The Mongolian Attack, and neutralizes a few of the attacks white had planned, had e6 not been played, it is like the triple variation of The Sicily, but without c5, and black has an extra tempo, Nf5 no longer threatens the same stuff it did back in the sicily, and can be instantly neutralized with g6, seeing as black has his extra tempo.

One of whites best replies to 2. ...e6, is 3. e3, which opens up the queen and the bishop, seeking to develop more pieces, the position after e3 is said to be relatively equal for both players, with neither having an advantage neither player is able to perform a turn 1 f7 sacrifice due to white having lost his tempo and having defended the turn 0 sacrifice thoroughly enough.

after 3. e3, we are considered to be out of the opening.

After 1. ...e6 2. ...f5 ,Graven's Defense
Gravens defense is an opening for black consisting of the moves 1. ...e6 2. ...f5, it is a lesser played opening, frequently played by the person it is named after, The Mongolian Attack has a few lines when played against this opening.

The line (1. Nf3, e6 2. Nd4 f5) is "The Mongolian Attack, Gravens Defense".

One of white's options after 2. ...f5 is to play 3. Nxf5, which instantly wins a pawn, as the knight of f5 can not be captured at risk of opening the e-file, this is the Triple Variation, and white is considered somewhat better, as he is up a pawn and has a few threats, after Nxf5 black is able to kick the knight away with 3 different moves, g6, Qf6, and Qg5, after Qf6 white can play e3, which threatens checkmate on h5 (Qh5), however, this is easily defendable if black just captures the knight, Qg5 is slightly more accurate for this reason, as it defends against Qh5 right away.

Instead of moving his queen, black may play g6, which attacks the knight, but white can play the same reply as before, e3, and threaten mate in 1 if black captures the knight, after black properly defends this mate threat, with, perhaps, h5, we are considered to be out of the opening, and the position slightly better for white.