@chess_feed Because if you promote to a queen it leads to stalemate after taking their queen.
B8=Q, Kg1
Qxf4 1/2
The under promotion can lead to checkmate.
@GMIgorSmirnov Stops the h pawn from promoting. If ignored and the pawn promotes Ng3 forks the king and new queen. If king takes, white has a7 and black is in zugzwang. Move the king, you can't promote or promote anyway and get skewered. Anything else loses to Nf2.
@xxChessMaster It is a checkmate, just not for white lol.
Rd5#. Blocks the check from the white bishop, reveals the check from the black bishop, and cuts off the white king's only escape square from the check.
@ImShahinyan Kb5, Kc3
Kc5, Kd3
Kd5, Ke3
Ke5, Kf3
Kf5, Kg3
Kg5, zugzwang.
If Kh3 or Kf3, Kf4 or Kh4
If Kg2, Kg4 to keep opposition.
The pawn promotes.
Kc5 first is wrong because then you're the first one to the g file and it's a draw. Any other move and it's a draw.