I know Sam and others often prefer to work in a vector format. Procreate does not allow that, so images must be moved to other programs and modified. Adobe Illustrator Draw is now available for free at the App Store. It has no where near the drawing capabilities of Procreate, but for simple clean line-work it may be a good tool for working up transfers. I've not had much chance to test it yet but it looks promising for a vector program.