## Batch, 226 bytes

    @set z=ABCDEFGHIJKLMNOPQRSTUVWXYZ
    @set a=YXWVUTSRQPONMLKJIHGFEDCBA
    @for /l %%i in (0,1,25) do @call echo %%z:~0,%%i%%%%z:~%%i,1%%%%a:~-%%i,%%i%%
    @for /l %%i in (24,-1,0) do @call echo %%z:~0,%%i%%%%z:~%%i,1%%%%a:~-%%i,%%i%%