Same as the topic in Final Fantasy I but this is for the monsters I'm missing in II
051
074
081
131
137
051- Gigantoad, Diest cavern(I think) and cave of Mysidia
074- Sand Worm, Palamecia desert
081- Green Soul, Chest in Diest Cavern, also found in the basement of castle Fynn
131- Pyrolisk, Unknown cave
137- Beast devil, ditto