I didn't use anything special really, just a regular old HB 2 pencil on some canvass type paper (or sketchbook paper, it's a bit thicker/grainier than most). I took a picture with my camera, tweaked some of the colours in photoshop (the lighting in this room gave it a blue tint).
I should have been a bit clearer in the intro paragraph, sorry. When I said "Yokai/japanese ghosts/monsters" that was just me listing synonyms. So basically yokai are japanese demons or ghosts, however you want to think of it. "Gazu Hyakki Yakou" is basically a listing and illustration by Toriyama Sekien of a hundred of these 'yokai'.