This boss is located at the end of the 'Africa' act in the mission 'Sphinx'.
This is a standard boss battle where shooting at the boss damages it's health. Be sure to place two or three emplacements down around yourself to watch your back as you attack the boss. Like all bosses it has three health bars, once a health bar level is destroyed it will retreat for a short amount of time and send variants of Monovisions to attack you.
Any weapons that inflict massive damage (Artillery, Snipers) is recommended.
This achievement requires you to kill it with more than one player in Co-op.