Execute Script on Shutdown (systemd)

To execute a script on every shutdown with systemd, create a service file with the content:
(on-shutdown.service)

[Unit]
Description=Will be executed on Shutdown

[Service]
Type=oneshot
RemainAfterExit=true
ExecStop=/usr/local/bin/youscript.sh

[Install]
WantedBy=multi-user.target

Put it inside the /etc/systemd/system folder, and enable it with:

systemctl deamon-reload
systemctl enable on-shutdown.service --now