Omega Ruins: all unique to the Ruins, you must activate the Ruins on the Search grid, and capture one or more monsters there; none of these monsters appear elsewhere, except for Adamantoise, which are listed under Inside Sin; Defender Z is machina and cannot be casptured
Zaurus
Floating Death
Black Element
Halma
Puroboros
Spirit
Machea
Master Coeurl
Master Tonberry
Varuna

Cavern of the Stolen Fayth: all unique to the Cavern
Yowie
Imp
Dark Element
Nidhogg
Thorn
Valaha
Epaaj
Ghost
Tonberry (found in the back of the cave)