I'm playing as white, and look at this absolutely BEAUTIFUL game
1.e4 d5 2. exd5 Qxd5 3. Nc3 Qd8. This is a standard Scandinavian, either my opponent actually studied it or just thought "me push pawn me push pawn", but so far standard opening.
Nf3 e6 5. d4 Bb4 6. Bd2 Bxc3 7. Bxc3 Nc6. As a GothamChess subscriber, after my opponent went Qd8, I tried following opening principles and I think I suceeded. Since I had a d pawn, I would want to push it to take as much space as possible, but I had to prepare it with Nf3 so it wasn't taken with the queen immediately. Him playing Bxc3 was a mistake since normally, you don't want to trade a bishop for a knight and it actually added protection to my pawn after my own Bxc3.
Bc4 a5 9. O-O a4 10. Ne5 Nxe5 11. dxe5 Bd7. Here, with the knight and bishop traded, I tried to further develop by putting my bishop on c4 and castling, which was made a lot easier by my opponent playing a5 a4. I have no idea what their idea was because it basically gave 2 moves back to me, he was letting me develop and castle without developing himself. My logic for Ne5 is if he takes (which he did), after dxe5 not only do I have a good pawn taking space defended by the bishop, but also the vision of the queens would be opened up and they would be staring at each other. If he took my queen, I would play Raxd5, and now I have developed my rook to an open file in the middle. If he didn't take the queen then I would take myself, which would make him lose the right to castle.
Qe2 b5 13. Bxb5 Bxb5 14. Qxb5+ Kf8 15. Rad1 Qe8 16. Bb4+ Ne7. Instead of taking the queen and playing Bd7, he blocked the vision of his queen ending the staring contest. After Bd7 I played Qe2, and my logic for Qe2 is I develop my queen and also open up the d file for my rooks, while also stopping b5, but I didn't realize that in game. However, the 600 ELO kicked in for my opponent and he played b5 anyway, which simply loses a pawn which was the deciding blunder in the endgame, so then I realized Qe2 stopped that move so after Bxb5 Bxb5 Qxb5+ and Kf8, not only am I up a pawn but also I forced him lose the right to castle. Rad1 was a simple developing move moving my rook to the open file with tempo on the queen. After he played Qe8 I gave the check Bb4 because it forced him to move his knight to e7 where it is pinned and in a bad position, but also if he is not careful, can potentially lead to back-rank mate.
Qxe8+ Rxe8 18. Rd2 g6 19. Rfd1 Kg7 20. Rd3 Nc6 21. Bc3 Rd8 22. Rxd8 Rxd8 23. Rxd8 Nxd8. This was a big trade and one that was not beneficial to my opponent because he is down a pawn. I played Rd2 to double up on the d file with back-rank intentions. I assume my opponent played g6 to prevent back-rank mate, and I played Rd3 to put my bishop on d2 to cut off the king's escape to h6 effectively locking the king in jail. However, before I could do that, he played Nc6 attacking my bishop, and I couldn't go Bd2 because then I would lose the pawn on e5, so I played Bc3 to defend. After Rd8 and the big trade, I was completely winning because one, I am up a pawn. Two, I had a bishop and he a knight, and bishops are better than knights. Three, his knight was in a bad location on the back-rank, whereas my bishop was more active.
f4 Nb7 25. b3 Nc5. 26. bxa4 Nxa4 27. Bb4 c5 28. Ba5 Nb2 29. Kf2 Nc4 30. Bc3 Kh6 31. g4 g5 32. f5 Kg7 33. f6+ Kg6. Now we transition into the endgame, and this is the best part of the game. I played f4 to further protect my pawn on e5 since I will of course have to move my bishop later. From here, I traded pawns and for some reason my opponent played c5 attacking my bishop for no reason, and after Kf2 activating the king and two waiting moves, he played Kh6 trying to get the king involved by taking a shortcut to the middle of the board. g4 was the critical move here, completely cutting off the king from the middle, and after 31. g4 g5 32. f5 Kg7 33. f6+ Kg6, I was very happy to shut down the king side because his king is completely in jail and would take minimum 8 moves to come into the game assuming I don't move, forcing all play to be on the queen side where I have a passed pawn.
a4 h5 35. Kg3 h4+ 36. Kf3 h3 37. Ke4 Na3 38. a5 Nb5 39. Kd3 Nxc3 40. Kxc3 Kh7 41. a7 Kf8 42. a8=R#.
This was completely lost for black because after Nxc3 and Kxc3, the black king had no way to stop my a pawn, it will promote regardless what black does. My opponent trading the knight for my bishop was the fatal mistake because with the knight, maybe he could potentially survive a bit longer, but still wouldn't work because given enough time, I would placed my bishop on b4 or a3 getting rid of the c5 pawn, and this bishop would've covered the f8 square which would've been the only way for black's king to get in the way. With the bishop preventing the king's escape, I would've escorted my pawn and promoted and delivered mate.
The moral of this game is that a single pawn can make all the difference in the end. 12. b5 turned the game from equal into a lost endgame.