I drew all of these with a .7 HB mechanical pencil, inked with a .7 V7 Pilot pen and the grey was a C5 Copic Ciao marker. Occasionally a broader tip black marker or a C3 Ciao Copic would get picked up and used.
With so little time to get these done I ended up with a real pressure to get at least 6 of these done every time I had a spare hour, which meant things like erasing had to go unless really needed. Or kneaded -- I used a kneaded eraser to lighten the pencil lines a few times as well.
Bad pun, there -- sorry.