Bonsai is an excellent art for an immortal. Dosed with their own strain of medichine, special breeds of tree will never die. Many intend to maintain a tree forever, taking records of its ever-shifting form, the display of which brings suddenly to mind who they were when it was that shape.
Anything that grows has been used as a form of bonsai. Numerous types of plants have been experimented with, of course. Corals are popular on aquatic habitats. Living bones and antlers, carefully engineered for unlimited, shapeless growth, are bent and bound into complex sculptures. Certain crystals can be coaxed into growth with the right mineral bath, growing around certain materials and away from others in expressionist fractals. On Legba, even fetuses are manipulated, with careful surgeries to design their grown form.