Another theme might be adventure. They could be on a journey through a magical forest or some other fantastical setting, facing various challenges together. This gives a lot of room for action and excitement in the stories. Also, there could be themes related to self - discovery. As they interact, they might learn more about themselves and their own capabilities. For example, the wolf might discover a more gentle side of himself, and the snake might find that he can be more social than he thought.
Well, Mr. X in the Times story might be a key figure whose identity is gradually revealed as the story progresses. Maybe he's a hidden source of information or a surprise antagonist.
I'm not sure about a specific one off the top of my head. But you can check out some popular fanfiction websites. They usually have a search function where you can type in 'leon x mr x' and browse through the results. Look for ones with high ratings and lots of reviews.
There could be a fanfiction where mr wolf and mr snake are partners in a detective agency. They use their unique skills, with mr wolf's strength and mr snake's stealth, to solve mysteries in their city.