A TRUE DRAGON TAIL
I'm going to tell you my favorite story from Commander 2017.
As I mentioned earlier, a new challenge in design was figuring out how we wanted to include cycles of cards in our decks. We definitely wanted at least one uncommon cycle that showed up across multiple decks. (In Commander sets, an uncommon shows up in multiple different decks, but not all of them.) But there was a problem: if we wanted to make it a creature, it would have to fit into the creature types of the deck. With almost no exceptions in all the decks, every creature in each deck are of its tribal type.
So, how could we have cycled out creatures then?
Our first thought was doing new changelings, like on Lorwyn. We tried that for a little while, and it worked okay, but played a little strange and didn't feel that unique. It also wasn't significantly adding to the goal of helping out other tribes since they were pretty generic cards that just happened to also have changeling. What we really wanted to do was put two creature types on one card and then put that into both decks.
We looked at all the different combinations, and they actually all fell into place. They could all be plausible. Except for one. There was one that was surely too crazy to work.
A green Cat Dragon.
Most of the team felt like that was a dead end. But, just to chase this as far as possible, I wanted to at least talk with Kelly about this. Maybe, just maybe, if I pushed hard enough, he'd find an agreeable solution.
So I walked over there. The conversation went like this.
Me: "Okay Kelly, so instead of changelings we are interested in doing these overlapping tribe cards."
Kelly: "I like doing something else than changelings from a creative perspective, definitely. What did you have in mind?"
Me: "So, these would combine two creature types on one card. We mapped it out, and it works pretty well for most of them. Natural even. But there is one combination that is . . . a little odd."
Kelly: ". . . Go on."
Me: "So I know this is kind of ridiculous. And there's probably no chance. But maybe, just maybe, if we could make it work somehow, on the absolute off chance you think it is possible, is there any way we could do a . . . (dramatic pause) Cat Dragon?"
Kelly, without missing a beat: "Oh, that's easy. Those already exist on Dominaria."
Me: ". . . What."
Kelly: "You mean you haven't heard the great tale of Wasitora and Umezawa? Oh, let me tell you a story . . ."
20 minutes elapsed, and I definitely missed my next meeting.
Kellypedia, to the rescue!
It turns out that ages ago, in the Legends novel, Tetsuo Umezawa was called in to take care of Wasitora, who was harassing a village. They fought, and the conclusion was . . . Wasitora would defend the city, and be paid in fish to do so.
Yes, paid in fish. Look, old Magic story is a wild place.
I will never forget the look on my team's face when I came back and told them Cat Dragon was a legit thing. I think they thought I was making it up, until I started going into the story.
The deal I made with Kelly was that we could do a Cat Dragon that was a member of Wasitora's brood and put it into both the cat and dragon decks, as long as we also put Wasitora into the Dragon deck.
Time and time again, through the whole design process, all the way to showing it off to development the Cat Dragon was questioned. And rightfully so: it sounds ridiculous. But my team was on board with the idea, and slowly but surely, we ended up getting most other people into the idea too.
Eventually, in development, the uncommon Cat Dragon was cut. (Though there is still one of the dual-type cards remaining among the decks. Keep your eyes out!) But, by this point, everybody was too in love with Wasitora (who had to be Jund) to take it out of the Dragon deck. We had sold the idea of a Cat Dragon so well that its legacy lingered on, even long after the reason it was put into the set at all was removed. And it made it all the way to print with gorgeous art by Cynthia Sheppard.
I give you: Wasitora, Nekoru Queen!

If she hits you, she demands fish as tribute or she'll send one of her brood after you.
Speaking of her brood, check out one of the cutest tokens in existence:

And that's the story of how we ended up with a Cat Dragon in the Dragon deck in a product that contains both Cats and Dragons long after the reason for it to be there was gone.
Hopefully, you all find it as adorable and endearing as I do.