Here are all the enemies in Phantasy Star III that are listed in the ROM but I can't find anywhere in the game :(

Enemy Name          Where they might be
----------          -------------------
Imp                 3rd generation
Shiek               3rd generation
Gryphon             Nial's quest, 3rd generation
Jumpliz             Nial's quest, 3rd generation
Skeleton            3rd generation, Sage Isle
Spectre             3rd generation, Sage Isle
Flutter             Mystoke Castle, Shusoran
Wirebot             Ayn's quest, 3rd generation Landen 
Guardbot            Ayn's quest
Disker              Ayn's quest, 3rd generation 
Twistbot            Ayn's quest
Swivlbot            Ayn's quest
Rotabot             Ayn's quest
Finis               Ayn's quest, 3rd generation