Litwick is obtainable first
There are only five ghost type Pokemon that are recruitable and that is the litwick , and the yamask line, the one you can get first is Litwick as he is found at forest grotto
But you can also find him in, Mountain Pass,Desolate Canyon, Inflora Forest, Breezy Plains,MirageSands, Smoking Mountain and the Skill Treasury. He is found on all floors in forest grotto.
Source 1
Source 2
