Here is the full list of all 22 Ex-Zodiac achievements.
Infiltrated level 4 of Zodiac's security system
Infiltrated level 3 of Zodiac's security system
Defeated Bazz and his deforestation machine
Infiltrated level 6 of Zodiac's security system
Defeated Commander Brutus and his enforcer mech
Infiltrated level 5 of Zodiac's security system
Defeated Dr.Fathom and his octo-mech
Defeated Ramses and his ancient, hijacked technology
Defeated the evil "space wizard" Thorn and his rock crusher
Infiltrated level 2 of Zodiac's security system
Defeated Slithe and his geothermal tunnel boring machine
Infiltrated level 1 of Zodiac's security system
Outpost Epsilon - S Rank
Impactor - S Rank
Devastator - S Rank
Defeated Titanox