For this challenge, the first thing I did was to drop the executable into IDA and give it a run with a debugger.
And there’s the flag: flag{this1isprettyeasy:)}
For reference, here were the actual instructions:
.text:01131000 _main proc near
.text:01131000 call ds:IsDebuggerPresent
.text:01131006 test eax, eax
.text:01131008 jnz short loc_113101F
.text:0113100A push 2 ; uType
.text:0113100C push offset Caption ; "Flag"
.text:01131011 push offset Text ; lpText
.text:01131016 push eax ; hWnd
.text:01131017 call ds:MessageBoxA
.text:0113101D jmp short loc_113105C