This file is a legal .cmd script and a legal powershell script.

sample.cmd

@(echo off) > $null 
set null( New-Module -ScriptBlock { function goto { }; function :{ } } )#= 

: # This file is both a .cmd script and a powershell script. if you save it as 
: # sample.cmd and run it it from cmd.exe it will run the same as if you 
: # saved it as sample.ps1 and run it.
: # well, in this case, I added some echos on the cmd side...

goto :CMDSTART

write-host -fore green this is powershell
write-host -fore blue thanks!

: CMDSTART <#  

doskey #=rem
if exist $null erase $null

echo this is cmd
echo and now I will call this same file as a powershell script

:: you can use powershell or pwsh, it's all good 
powershell -noprofile -executionpolicy unrestricted -command "iex (get-content -raw %~dfp0) "

echo and finishing as cmd
: #>

sample2.cmd

@(echo off) > $null 
if #foo NEQ '' goto :CMDSTART
($true){}
# powershell script starts here 

write-host -fore green hi from powershell

return 
:CMDSTART
:: do anything we need to before calling into powershell
if exist $null erase $null
echo hi from cmd.
powershell -noprofile -executionpolicy unrestricted -command "iex (get-content -raw %~dfp0) "

I worked a bit more and made it better!

The second example is much less tricky!