Here is the full list of all 18 Ex-Zodiac achievements.
Infiltrated level 1 of Zodiac's security system
Defeated Bazz and his deforestation machine
Defeated Slithe and his geothermal tunnel boring machine
Defeated the evil "space wizard" Thorn and his rock crusher
Defeated Ramses and his ancient, hijacked technology
Defeated Dr.Fathom and his octo-mech
Defeated Commander Brutus and his enforcer mech
Infiltrated level 2 of Zodiac's security system
Infiltrated level 3 of Zodiac's security system
Infiltrated level 4 of Zodiac's security system
Infiltrated level 5 of Zodiac's security system
Infiltrated level 6 of Zodiac's security system