It's my birthday! I'd like to invoke the rite of trivia about my first ever mythic rare I opened, Grimgrin Corpse-Born. Or Innistrad zombies in general.

The original plan was the “leader” of the zombies would just be Army of the Damned (the card that could make twenty-six zombie). The idea was that the zombies didn’t have a leader; they were just a lot of zombies. But set design felt there needed to be a legendary zombie, so they made one.Happy Birthday!

A friend of mine cast Army of the Damned and we had 13 different zombie tokens on hand for him to play. Very much a flavor win and something we've been waiting to be able to do. Can you give high fives to whoever was responsible for making so many zombie tokens on different planes?

Will do.

Can I get some birthday trivia on my favorite card, Grimgrin, Corpse Born?

In design, we wanted a “big bad” for each of the monster types. The design team’s card to fill this void was Army of the Damned assuming the worst zombies is a giant horde of them. Development decided zombies should have a singular named “big bad” and made Grim Grim. Happy Birthday!

How do you decide seemingly arbitrary values in instances like Tragic Slip's -13/-13 effect or Army of the Damned's 13 Zombies or Into the Maw of Hell's 13 damage? Is 13 commonly used to represent a big number because it's perceived as an unlucky number, or does this come out of playtesting as an ideal choice in these cases?

13 was a theme of Innistrad because it’s a symbol of bad luck.

Not a question, more of a "thanks for everything you do" with a story, since I know most of these cards are your designs. In a Magic Online standard game, thanks to Parallel Lives, Endless Ranks of the Dead, Army of the Damned, and Craterhoof Behomoth, I attacked my opponent for 5727 damage, and it was beautiful. My only regret was the other 52 of my 108/108 trampling zombies still having summoning sickness.

I enjoy stories like these.  Thanks.

I have a choice between Zombie apocolypse and Army of the damned in my zombie deck. Which one should I choose?

It depends on what your deck does. Army of the Damned is a stronger card powerwise but Zombie Apocalypse is, well called Zombie Apocalypse so it wins on the flavor front. I found room for both in my zombie deck.

At what point in Innistrad's design was Grimgrin made? Everybody seems to have forgotten Army of the Damned was actually "the Zombie mythic" because Grimgrin looks more in line with Olivia, Geist and Mikaeus. Do they have nothing to do with each other?

I believe Grimgrim was actually designed during development. The file turned in from design had Army of the Damned as the “zombie mythic”.