There aren't a huge number of shapes and characters that easily lend themselves to being handpainted on a ball ornament. Anythign with a boxy shape is going to look too Mercator-y, not natural. Anythign too round is probably already out there in ornament form if you go looking -- billiard balls, globes, snowmen.
That's one of the things that makes this cute four-pack of balls, all based on Mario enemies, so much fun. The Chain Chomp, the Bob-Omb, a Boo, and a Piranha Plant. All naturally rounded, surprisingly since they came fromt he eight-bit era where square shapes were just easier to pull off. And unlike certain other Chain Chomp Etsy items, this one won't bite off your privates.