At conventions I sometimes accept little headshot/portrait commissions (either of your own monster/dragon OCs or I create a monster/dragon OC for you based on your vibe and/or things you like), that I draw with ballpoint pens, pencils and gel pens during the con.
Just come by, tell me what you want me to draw (for your own OCs I require visual references; if I shall come up with something for you, no visual references are needed), pay, and come back later to pick up the artwork.
Above, there are some examples (outlines/shaded options are available) of what to expect, and on the left is a commission I drew during a con in summer.