You might need to install aplay to get this to work, not sure what you're using to play WAV files. Use:

	sudo apt install alsa-utils

to install aplay.

The first script is what you'll run with the Mystic menu command GY, make sure the second script is in the same directory as the first script, usually /mystic/themes/default/scripts


############## login_wav.mpy ##############

import mystic_bbs as bbs
import subprocess
import os

# Path to this MPY script
path = bbs.param_str(0)
dir_path = os.path.dirname(path)

# Worker script and WAV file
player_script = os.path.join(dir_path, "play_wav.py")
wav_file = "/mystic/56k_mdm.wav"

# Suppress output so nothing leaks into the BBS session
devnull = open(os.devnull, "w")

# Launch the worker and immediately return control to Mystic
subprocess.Popen(
    ["python", player_script, wav_file],
    stdout=devnull,
    stderr=devnull,
    close_fds=True
)


############## play_wav.py ##############

import sys
import subprocess
import os

def play_wav(wav_file):
    if not os.path.exists(wav_file):
        return

    # aplay blocks, but that's fine because this script is detached from Mystic
    subprocess.call(["aplay", wav_file])

if len(sys.argv) > 1:
    play_wav(sys.argv[1])