Is there anything in the rules stopping Ward costs that give opponents (ie the controller) something instead of paying a cost? Like "Ward - Each other player draws 2 cards". Or "Ward - Each other player searches for a basic land. It enters tapped and then they shuffle."

Yes. Wards, by definitions, have to be costs.

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.

About the clowns: it’s impossible to say whether a non clown card would ever be drawn because the question is under specified. With an infinite deck of cards, it’s not sufficient to simply say you “shuffle” them as you would a finite deck. Normally, this implies a uniform distribution, which is impossible with infinite cards. Therefore we must define some asymmetric distribution over the cards. So yes, with some distributions you would expect to never draw a non-clown (as an aside we also bump into the axiom of choice here: with infinite identical clowns, is it even possible to identify a specific one?). But we could also pick a geometric distribution while shuffling, with a probability p that each card (in order drawn) is a non-clown. Then we would expect to see a non-clown in just 1/p draws!

It still happens with great infrequency.

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

Hey Mark. Does blue get to shuffle creatures into libraries now?

Not really, no. Yes, there is a card in Murders in Karlov Manor that does. Not a precedent.

If/when either make a card that lets us search and then not shuffle or integrate shuffling as part of searching.

I’ve tried to make shuffle an inherent, and unwritten, part of search, but haven’t, as yet, been successful. If, but I hope when.

Hello Mark. I redeemed my coveted birthday rite several days ago, but it seems to have gotten caught up in the shuffle. I figured I wouldn't submit it on my birthday, which was the 6th, because a lot was going on then in Magic. My query was for any interesting tidbit about my favorite card in the game, Malefic Scythe from M21, and, provided you had nothing about it, instead the card that got me into the game, Errant Ephemeron from Time Spiral. Thank you very much for your time and consideration.

When we first designed suspend creatures, we started with familiar vanilla and French vanilla ones. Errant Ephemeron was Air Elemental, and one of the first ones we designed. Happy Belated Birthday!

If we can't destroy the battlefield why can we shuffle our graveyard into our library? that is also doing something to a zone

You can move cards from zone to zone. That is a different thing than destroying a zone.

If you can destroy it, you can exile it, but what about "shuffles it into their owner's library"? Thinking about cards like Oblation or Deglamer. Can any color shuffle away a permanent type so long as they could otherwise destroy it?

Not normally, but I wouldn’t call it off limits if there’s a larger set theme.

When you're playtesting at work, does the team do anything to avoid mana flood/screw? Or do you let it happen to see how test cards work in those situations?

If it’s early and we’re not testing environment, we’ll just shuffle and draw a new hand. If it’s later when we are testing environment, we play like you all would play with normal mulligans.