Would a black spell or effect that lets you take control of a permanent be an acceptable bend? I know taking control is usually blue or red, but it doesn't feel like a break because black can already cast other players' spells.

We let black mess with other people’s stuff, but more often from the graveyard or their library.

Is there a reason why you seem to no longer print cards with the "when this is put into your graveyard, shuffle yard into library" text from the original elldrazi titans? It feels like a major part of their identity to me, and i was a bit sad to see that none of the titans in MH3 had it.

It doesn’t play well.

Could white get "everyone shuffle their graveyard into their library", and if not, what would the philosophical reason not?

No, it’s not a white ability. Mechanics are isolated into colors to make the game play better, not because we couldn’t come up with a way to justify it philosophically.

"we shouldn't [allow casting exiled cards]"What about putting exiled cards into your graveyard or shuffling them back into your library? Is there a sufficient number of extra steps or hoops to jump through to get your cards back from exile?

For me, no. Exile is an important tool to permanent get rid of cards. If we don’t want to permanently get rid of them, we can just destroy them.

Countably infinite does NOT mean finite. If you shuffled an infinite number of Clown tokens into your library, you would never draw another kind of card in that game. Infinity plus however many cards were in your library is still infinity. Imagine if you didn't shuffle. How many cards would be on top of the first real card? Infinite cards are on top, so you'd never draw the card. If you shuffled the deck, that would still be the case. There would be an infinite number of Clown tokens before and after each real card, because the chance of getting a Clown token between any two cards while shuffling is 100%. Not 99%, not 99.999...%, just 100%. Infinity divided by the cards in your library is infinity. You can never draw any real cards, because even if you took off the top card, infinity minus one is still infinity.Grenzo, Dungeon Warden would always hit, since there are an infinite number of Clown creature token cards on the bottom of your library. Since tokens have 0 mana value, you can't cascade into any real cards. You could mill out if you got hit by Tasha's Hideous Laughter. If you chose Land for Abundant Harvest, you would get one if you had a land in your library. However, if you got hit by Cut Your Losses, you would only mill Clown tokens, and no cards from your library. Infinity plus the number of real cards in your library divided in half is infinity, so you'd never get to the first real card, and you'd still have an infinite number of Clown tokens on top. Finally, if you happened to play Braingeyser with X equal to infinity, you would STILL not draw any real cards. Infinity minus infinity is infinity. You would have an infinite number of Clown tokens in your hand, and an infinite number of Clown tokens on top of your library.It's easier if you think of infinity as a description or a quality rather than a number. Treating it like a number infects whatever math you're doing with odd-looking results.

FYI

Hello Mark! As part of White's "taxing / delaying the casting of a spell" effects such as Anointed Peacekeeper, Elite Spellbinder, Reprieve, etc., would White be allowed in-pie to put a card from an opponent's hand into their library N cards from the top? Sort of like a "You still get to play this card, but not for a couple turns" effect.

No, putting cards X from the top is something we do in blue rather than white.

What color gets the smallest subset of things it can play off the top of its library?

That is not something I know off the top of my head. We try not to make subsets too small, otherwise it’s never relevant.

Hey maro any chance we can slow down on all the cards that steal from your opponents library? Very exhausting and feels bad when your opponent is constantly stealing your spells.

It is an effect we’re looking seriously at. We don’t like that it discourages playing big, fun cards.

Could white get “Put target spell on the top or bottom of its owner’s library”?

No.

Can libraries be flipped upside down? (The top and bottom are reversed; the 'top' card is automatically revealed to all players, etc.)If not, what kind of problems do you expect?

I don’t believe so, for both rules reasons and logistical reasons. Also, having hidden information is important to good gameplay, so even if there were no other issues, I’m skeptical we’d do it.