If you want to add additional screensavers in Linux Mint Mate edition use the following commands:
sudo apt-get install xscreensaver-data-extra xscreensaver-gl-extra
cd /usr/share/applications/screensavers
sudo perl -p -i -e 's/OnlyShowIn=GNOME;/OnlyShowIn=GNOME;MATE;/g' *.desktop