Warning: I have read sysvinit is unmaintained in newer Debian releases. If unmaintained sysvinit is better for you than SystemD, please continue.
To install sysvinit on a Debian distribution run the following commands as root or with sudo:
apt-get -y install sysvinit-core shutdown -r nowThat is all you have to do. Do not worry about the "Processing triggers for systemd..." message.
This has changed your init to sysvinit. SystemD will still be installed but if it does not run as PID 1 it is harmless.
Removing the systemd package and those related to it is a different job and is not addressed in this document.
You can follow the instructions on using the angband.pl Debian repository on from that site.