Can you invoke help flags for a tool or binary? This program has extraordinarily helpful information...
The challenge gives us a link to download a 64-bit ELF Executable file named "warm". Trying to run it with:
./warm
in a linux terminal gives us this output:
Hello user! Pass me a -h to learn what I can do!
Passing in a "-h" to the program as it asked us to do gives us a different output with the flag. Final command:
./warm -h
picoCTF{b1scu1ts_4nd_gr4vy_30e77291}