I went out for about 6 hours and got enough candy for 3 Gengar. Cubone everywhere too. Drowsee is about as common as always here.
For things NOT Halloween I got 1 Dratini, 2 Machop, 2 Squirtle and 1 Nidoran Male. I can't remember seeing any Pidgey and I saw 2 Ratatta, 2 Zubat and 2 Weedle. I'm just listing those to juxtapose against the 100s of Ghastly/Cubone/Drowsee. It's madness. We ARE going to get sick of Gengar/Cubone/Drowsee over the next week, I suggest sticking to nests only if possible since they still spawn their usual.
However, walking and hatching are ridiculous now. Buy incubators and walk all those pokemon which are nearly evolved. Even 20 Pikachu candies were no trouble.