Gengar and its evolution family were the only Ghost types, and they were special, so why did they make Gengar’s STAB moves unusable?
Lick makes contact. So Ghost was probably physical because Lick makes contact, and most physical moves make contact.
Night Shade deals damage depending on the user's level and the target's HP, it doesn't matter if it is physical or special. Doesn't it bypass the user's offensive and the target's defensive stats? That's why Pokemon like Registeel, Chansey, and Xatu use Night Shade/Seismic Toss.