I spent the last week or so working on this toad. It was drawn on an 2017 iPad Pro 10.5 using the Apple Pencil and the Procreate app. I used mostly airbrushes in the app but did dabble with a couple of others. The reference photo was one I had taken of the frog sitting in a bird bath.
Here is a link to a time lapse of the drawing. The Procreate app does a great job of storing the video of the work. It may be helpful to some to see how the drawing is done.