Which one?
Some suggestions for variants

In my fantasy world of anthropomorphic musical instruments, Crowned Knight, Bishop and Rook aren’t even fairy chess pieces though official chess play only sees them as a promotion of a pawn or the corresponding regular piece.
Promotion should be more flexible: it would be better if we could define promotion for non-pawn variants and select specific squares for promotion for each player, that would already add tons of possibilities for variants
it would be really cool if we had more fairy chess pieces, these are some of my suggestions:
Crowned Rook: Rook + Ferz
Crowned Bishop: Bishop + Wazir
Wizard: Ferz + Camel
Champion: Wazir + Alibaba
Modern Elephant: Ferz + Alfil
Woody Rook: Wazir + Dabbaba
Xiangqi Cannon: moves like a Rook but it must jump over one piece to capture
Crowned Chancellor: Chancellor + Ferz
Crowned Archbishop: Archbishop + Wazir
Zebra: (3,2) Leaper
Bison: Camel + Zebra
Buffalo: Knight + Camel + Zebra
and many more…
it would also be cool if we could set KOTH squares for each player, for example: a variant where if the white king reaches the 8th Rank then white wins, if the black king reaches the 1st rank the black wins