Cops: Make a regex - Make a snake
05AB1E, Cracked by mbomb007
Hopefully fun to crack and not too obvious.
Regex (PCRE):
^\w*[+\-*\/%]*\w*.{0,2}$

Output n=4:
[[1, 2, 3, 4], [8, 7, 6, 5], [9, 10, 11, 12], [16, 15, 14, 13]]

Original solution
UXFXLNX*+NFR}ˆ