1. c8=T! ... 2. 0-0-0#! (wTc8->d1)

Reprint+History Of The Idea-https://www.ecforum.org.uk/viewtopic.php?f=2&t=10857&p=246851#p246851
https://www.chessproblem.net/viewtopic.php?t=232

Created by the user mrmip

https://www.chessproblem.net/viewtopic.php?t=232

It still seems that there are castling loopholes in chess variants.

The rules for castling in Fischerrandom or 960-chess are:

" Castling, as in Orthodox chess, is an exceptional move involving both the King and Rook. Castling is a valid move under these circumstances:
Neither King nor Rook has moved.
The King is not in check before or after castling.
All squares between the castling King's initial and final squares (including the final square), and all of the squares between the castling Rook's initial and final squares (including the final square), must be vacant except for the King and Rook.
No square through which the King moves is under enemy attack.

The movement of the King and Rook during castling should be easily understood by players of Orthodox Chess:
When castling on the h-side (White's right side), the King ends on g1 (g8), and the rook on f1 (f8), just like the O-O move in Orthodox chess.
When castling on the a-side (White's left side), the King ends on c1 (c8), and the rook on d1 (d8), just like the O-O-O move in Orthodox chess.
Sometimes the King will not need to move; sometimes the Rook will not need to move. That's OK."

Now reading those rules as Devil reads the Bible the following seems possible:

(diagram)

Fischerrandom Chess, mate in 2. White king has not moved.
Solution 1.c8=R any 2.0-0-0 #

[White rook just moves to d1,all squares in the path c8-c1-d1 are free except for wK. The castling rook has not moved before ;)]

1. b8=D? Lb3!

1. Lxa2+! Kc2 2. b8=D Kxd3 3. 0-0-0#
2. ... e2,~ 3. Db1#
1. ... Kb2 2. b8=D+ Kxa1 3. Db1#
2. ... Kxa3 3. Lb1#,Lxc4#
2. ... Kc2 3. Db1#

https://www.chessproblem.net/viewtopic.php?f=7&t=60&p=2362