The card has been designed bottom up.
The first thing was coming up with a new cumulative upkeep cost and then everything has been designed around it, starting with the colors.
It had to be monocolored with an off-color cumulative upkeep because of the challenges, so it had to be an effect that could justify that. I explored multiple options but exiling cards from graveyards was the one that I thought the most elegant and easy to design with, so I went with it.
What colors could do that? White, black, and green. Blue and red have also done that but mostly only in sets with a graveyard theme, so I excluded them.
Out of the three Abzan colors, what could I make with that cost? An anthem effect in white immediately came to my mind.
At that point I chose to put the other two colors as hybrid mana in the cumulative upkeep, but then I thought I had to care about the exiled cards in some way to justify the cumulative upkeep cost. Then I made the mental connection anthem + number of cards exiled.
At this point, the card's only other ability was "Creatures you control get +X/+X, where X is the number of cards exiled with CARDNAME." It would have certainly been more elegant, but it clearly wanted to be a rare and I felt it lacked some splashiness. I also wanted to make the card even more clearly monowhite.
I tried granting two core white abilities like vigilance (conveniently also in green) and lifelink (conveniently also in black). At this point, the non-cumulative upkeep rules text was "Creatures you control get +X/+X and have vigilance and lifelink, where X is the number of cards exiled with CARDNAME."
But then it didn't feel right to me that creatures got pumped by noncreature cards too, so the text became "Creatures you control get +X/+X and have vigilance and lifelink, where X is the number of creature cards exiled with CARDNAME."
But then I asked myself what would have happened if you didn't have any creature cards to exile to the upkeep cost, would you just have to lose your enchantment? I wanted to find a use for noncreature cards and an incentive for you to want to also exile noncreature cards. It was then that I splitted the abilities and also went from +X/+X to "+1/+1 for each" for clarity. At this point the rules text was:
Cumulative upkeep—{B/G}, Exile a card from a graveyard.
Creatures you control get +1/+1 for each creature card exiled with CARDNAME.
Creatures you control have vigilance and lifelink if there are N or more noncreature cards among cards exiled with CARDNAME.
I started thinking about the value of that N. When I considered 4, I thought "Hey, this is really similar to delirium!" So I changed that ability to make it pseudo-delirium, but I couldn't label it "delirium" because it didn't check the card types among cards in your graveyard, but among cards you exiled, which is technically quite different, but that ability was meant to evoke delirium.
Finally, I thought about constructed. I realized this card was mostly useless there unless I gave it some immediate impact, and the very first idea was letting you exile a card immediately so that you could have it immediately do something. And so the final version of the card was born. I just had to find a flavor for it.
I struggled a lot with it. At a certain point, I remembered the card
Castle. It wasn't the exact same bonus, but it was still kind of an anthem effect. I still had to justify the graveyard part. I thought about the spirits of the buried rising up from the earth, infusing the tombstones and animating them, and the card could represent a bunch of these animated tombstones. The spirits represented the creature cards you exiled and the tombstones the noncreature cards. That felt good enough to me, but the castle idea for the anthem and the tombstones idea for the graveyard interaction just felt like two completely separate things to me. Was there a way to connect them?
Then a sudden memory of my childhood hit me like a flash. I've always been a big fan of the Duck side of Disney comics and such. You know, Donald Duck, Huey, Dewey and Louie, etc..., and last but not least Scrooge McDuck. I have not just read but devoured what in Italian is called "La Saga di Paperon de' Paperoni" (literally "The Saga of Scrooge McDuck", I don't know its actual English title, I have it in Italian), which is a twelve-chapter story by Don Rosa, all based on the works by Carl Barks, telling the whole life of Scrooge starting with his childhood in Scotland and ending with him in Duckburg as the richest duck in the world. I still read that from time to time. The very first chapter starts with Scrooge's father Fergus taking him to the castle of their clan and telling him of their heritage. Later in that same chapter, the now teenager Scrooge digs turf from the clan cemetery attached to the castle to sell it as burning fuel and gain a few bucks. I had the image of the young Scrooge looking at the clan castle in rememberance that takes more than half of the page clear in my mind. I thought that a cemetery attached to a clan castle was the perfect way to connect the two disjointed ideas I had, and as I thought of it, I immediately took that book from the library in my own bedroom and read again the first chapter, looking for how Don Rosa was calling that graveyard, because I didn't want to use the word "graveyard" in the card name because of its technical Magic rules meaning. It was always just called the "castle cemetery". I thought that felt like a good card name so I just went with that. As for the flavor text, it's also inspired by that story. In Disney Duck canon, Scrooge is really the last of the McDuck clan, and that's very relevant in many occasions. Scrooge doesn't have a sword, at least as far as I know, but I added that part to give it more of an adult fantasy feeling. The "spirits of your ancestors" represented the exiled creature cards and "blessing the blade of your sword" was meant to represent the granted keywords. It fit in MSE and I really liked it so I went ahead and posted it. I admit that it's not my most elegant design overall and that the flavor probably doesn't make too much sense to you if you don't know the backstory of Scrooge McDuck, but to me it was just a trip down memory lane, back to a time when I was way happier than now, and it all connected too well for me given how much I like that story. If any of you happen to also be fans of the Disney Ducks, Duckburg, and such, I strongly suggest that you check it out. It's from several years ago, maybe even a couple decades ago, so it might not be the easiest thing to find, but it's definitely worth a read if you can find it.