I guess I don't disagree with the crowd saying "make it available in a blackout!". I was really annoyed with Urza, Academy Headmaster. I also probably have a bias in that I know I always have plenty of dice, despite the fact that I don't own a smartphone. I figure that if d20 rolls are allowed, d12s are no problem, since you can just use a d20 and reroll higher numbers. A D8 might be a little less convenient.
Personally, I do think that rules should be written on cards so smartphones aren't necessary. I think the dungeon is an okay limited mechanic in the same way that contraptions are fine (it's a mini-game mechanic). But I hate the dungeon in proper games because it doesn't say what it does on the card. I don't like the monarch for the same reason. And I don't like that Old Gnawbone doesn't give reminder text for treasures.
I've used a d20 to replace a missing d12 plenty of times. It's clunky, but it doesn't take long compared to searching your library. I figure if you can use d20s on lots of cards, using a d12 on one or two in a commander deck is okay.
I don't get the fuss over a D12. If everyone is expected to have a D20, you can just roll until you get 12 or lower. I don't like adding game complexity, but compared to the dungeon mechanic, this is nothing. It's not like they're asking you to go to askurza.com or somehow know about massive erratas, or know exactly what everything on Garth One-Eye does without looking it up, or just have dungeon tokens on hand. There are other cards which ask far more than this one.
If you're playing cards that roll d20s, you should have some d20s on hand. But if you don't, it's not a big deal. The group will figure something out, and someone has a smart phone. The game already asks you to play cards differently from how they're printed because of erratas, and to know what mechanics do without reminder text. Figuring out how to roll a die is nothing.
Again, if you have access to a D20, you can always use it as a d12. You have a 40% chance of rerolling it, but it's not like rolling a die takes a long time.
Personally, I do think that rules should be written on cards so smartphones aren't necessary. I think the dungeon is an okay limited mechanic in the same way that contraptions are fine (it's a mini-game mechanic). But I hate the dungeon in proper games because it doesn't say what it does on the card. I don't like the monarch for the same reason. And I don't like that Old Gnawbone doesn't give reminder text for treasures.
I've used a d20 to replace a missing d12 plenty of times. It's clunky, but it doesn't take long compared to searching your library. I figure if you can use d20s on lots of cards, using a d12 on one or two in a commander deck is okay.
Low-power cube enthusiast!
My 1570 card cube (no longer updated)
My 415 Peasant+ Artifact and Enchantment Cube
Ever-Expanding "Just throw it in" cube.
If you're playing cards that roll d20s, you should have some d20s on hand. But if you don't, it's not a big deal. The group will figure something out, and someone has a smart phone. The game already asks you to play cards differently from how they're printed because of erratas, and to know what mechanics do without reminder text. Figuring out how to roll a die is nothing.
Again, if you have access to a D20, you can always use it as a d12. You have a 40% chance of rerolling it, but it's not like rolling a die takes a long time.
Low-power cube enthusiast!
My 1570 card cube (no longer updated)
My 415 Peasant+ Artifact and Enchantment Cube
Ever-Expanding "Just throw it in" cube.