/usr/share/applications/screensavers/demon.desktop is in xscreensaver-data-extra 5.34-2ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 | [Desktop Entry]
Name=Demon
Exec=/usr/lib/xscreensaver/demon -root
TryExec=/usr/lib/xscreensaver/demon
Comment=A cellular automaton that starts with a random field, and organizes it into stripes and spirals. http://en.wikipedia.org/wiki/Maxwell%27s_demon Written by David Bagley.
StartupNotify=false
Terminal=false
Type=Application
Categories=Screensaver;
OnlyShowIn=MATE;
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