Question: is milcery an overworld spawn?
Answer: Milcery's locations are Route 4 and 2 spots in the Wild Area. Route 4 is the easiest place to get Milcery because in the Wild Area it only appears during 1 weather condition while on Route 4 Milcery is always around. Milcery will not appear in the overworld the way you can see Yamper, Pumpkaboo, Diglett, etc.