Agumon and his evolutions, Greymon and MetalGreymon!
Painted this piece on an app called Colors! 3D for the Nintendo 3DS. Not sure how long it took but I know it was over six hours because undo horrifyingly becomes unavailable past that time.[link]
And here's a nice little video showing the process sped up.
It cuts off because, again, six hours.
Digimon, Agumon, Greymon, MetalGreymon © Toei Animation, Bandai