mods don't come to the forum anymore. It would be better if we all took a bit of moderation juice ourselves.
I can answer the OP questions:
1st Question:
Why was Bf2 move not a blunder upon engine check?
Answer:
The Bf2 move isn’t a blunder because White has Tactical Shots to keep the center pawns from being taken.
18. Bf2 Bxh4
19. Bh7+ Kh8
20. Bxh4
At this point, if black plays random move, white can retreat his LSB to safety and his center pawns are fine.
If Black plays g6 trying to trap LSB, Black ends up trapping their LSB on h5.
This allows white to play g4 maintaining piece equally.
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2nd Question:
What would the engine say if white doesn’t find the 19.Bh7+ move?
Answer:
Let’s say Blacked played 18...Bxh4 and white didn’t see the intermezzo move 19.Bh7+.
Lets say White plays the move 19.Bxh4 doing the normal recapture.
At that moment, the engine would give white a blunder/mistake mark.
The engine would say 19.Bxh4 is a blunder/mistake which loses 2 center pawns and white best move was 19.Bh7+ keeping the 2 center pawns.
————————
3rd Question:
Why after the the following moves:
18. Bf2 Bxh4
19. Bxh4 Qxd4+
20. Bf2 Qxe5
Is white with a +1 advantage even though he is down 2 pawns?
Answer:
White has a +1 advantage in this position because White has great piece activity + great coordination + bishop pair
It is true that Black has a material advantage!
Black won 2 pawns with his Queen, but in the process of winning those pawns black made sacrifices.
Black didn’t develop all his pieces.
Black didn’t improve his coordination.
If Black is able to consolidate his position by developing all his pieces + coordinating better, Black can begin winning!
If White messes around, The engine will begin to favor Black -2.
In this position, It is a Dynamic (White Player) vs. Materialistic (Black Player)
White wants to use his lead in development + better coordination to stir up trouble vs. Black King.
White being down 2 pawns doesn’t matter if the Black King is checkmated.
It is very common practice to sacrifice pawns or pieces in a checkmating attack.
All the pawns + pieces sacrifice don’t matter if you are successful.
Black, on the other hand, wants the position to become a boring King and Pawn Endgame.
Black wants all the pieces to be traded off the board.
If all pieces are gone, Black will win due to 2 extra pawns.
———————
Lastly, I will finish by saying the following:
These Dynamic vs. Materialistic battles can go either way.
You have every reason to be concerned!
It is very understandable.
You have to remember every chess player has their own tolerance level.
I have seen some players say they can’t play Caro Khan because they think it is boring and makes them fall asleep.
I have seen some players say they can’t play Sicilian Dragon because they think it is to stressful.
Every person is different.
The important thing is to try your best & keep asking those questions.
This is how we all get better.
@X_Player_J_X Thanks pal , best and only worthwhile answer I've recieved so far on the threat!
I also want to insert some analysis that I got upon consultation with a good friend of mine Chien Ming on skype (around 1800 fide rating) and 2000+ rated in lichess classical. Again this pertains to the line:
18. Bf2 Bxh4
19. Bxh4 Qxd4+
20. Bf2 Qxe5
21. Rfe1
