If you loved Rudolf the Black Cat, try Pokémon the Movie: Diancie and the Cocoon of Destruction
A bridge between a film you've already seen and one most people haven't. Here's what they share, and what the second one does that the first one doesn't.

Rudolf the Black Cat

Pokémon the Movie: Diancie and the Cocoon of Destruction
What they share
Both films are directed by Kunihiko Yuyama, and they both carry the cozy, playful mood tags, and they sit in Adventure / Animation / Comedy / Family territory. If that's the register that drew you to Rudolf the Black Cat, the second film will land in a comparable space — through a different lens.
What Pokémon the Movie: Diancie and the Cocoon of Destruction is
Here's another installment, for the completists. Diancie must leave her underground kingdom to save it. This quest brings her above ground and into contact with Ash, friends, and some diamond-obsessed thieves who accidentally awaken Yveltal. It's another day, another apocalypse narrowly averted by children and pocket monsters.