Shark, Shark, Baby (Functional)

Our toothiest friends are all grins—with Ikoria, Shark becomes a real creature type! Since there are no cards pointing you toward a Fish-tribal deck, and since "Shark Fish" just sounds odd in English, Doug Beyer made the call that Shark replaces Fish on the affected creatures. The only card that makes a Fish token, Reef Worm, produces a distinctly un-Shark-like Fish, so it stays as it is.

Affected Cards:

Battering Krasis: Fish Beast -> Shark Beast

Giant Shark: Fish -> Shark

Half-Shark, Half-: Fish -> Shark

Hammerhead Shark: Fish-> Shark

Shambleshark: Fish Crab -> Shark Crab

Sharktocrab: Fish Octopus Crab -> Shark Octopus Crab

Voracious Greatshark: Fish -> Shark

Fowl Play (Functional)

With the release of Unsanctioned, we decided that while Chickens are funny, it's more fun in gameplay if Chickens have the creature type Bird. This was a very clean word replacement across the board—but pay close attention to Chicken à la King. His Royal Eggcellency lets you tap Birds and puts counters on Birds now, and he's even become a Noble with the release of Ikoria!

Dryad of the Dryad Dryad (Functional)

Dryad of the Ilysian Grove in Theros Beyond Death was printed just as a Nymph. This was an oversight; it's now a Nymph Dryad.

Stand or Fall (Functional)

As the rules around multiplayer evolved and settled over time, Stand or Fall fell along the wayside somewhere along the line. The most correct interpretation of the previous Oracle text, ambiguity and debate aside, is that you'd choose some creatures for one opponent and no one else's creatures could block. Its new erratum brings its original and intended functionality back.

Stand or Fall was:

At the beginning of combat on your turn, separate all creatures defending player controls into two piles. Only creatures in the pile of that player's choice can block this turn.

New text:

At the beginning of combat on your turn, for each defending player, separate all creatures that player controls into two piles and that player chooses one. Only creatures in the chosen piles can block this turn.

Cast All the Things (Non-Functional)

The adventurer card mechanic from Throne of Eldraine shed a lot of light on something we had been handwaving linguistically with rules backup. When Garruk's Horde says that you may cast the top card of your library if it's a creature card, we don't really mean that. You can cast an artifact or land card if you cast it as a morph. You can't cast an adventurer creature card if you cast it as an instant or sorcery. We really mean that you may cast the top card of your library if you cast it as a creature spell. Similarly, Oracle of Mull Daya lets you play lands, not necessarily land cards that could be cast as a morph, from the top of your library.

When the rules for bestow changed in Theros Beyond Death, it removed the last edge case where it made a difference whether you were looking at the spell or looking at the card plus the various modifiers. With that difference gone, we decided to switch to more honest, friendly words. This doesn't change the existing rules interactions, but it might make you realize something that you didn't know.

In cases where it's ambiguous or sounds too weird, or where space simply doesn't permit, we'll still use the older template (notably Haldan, Avid Arcanist in the Commander decks). This change affects just over 100 cards. For example:

Garruk's Horde was, in part:

You may cast the top card of your library if it's a creature card.

New text:

You may cast creature spells from the top of your library.

Raid-light Savings Time (Non-Functional)

Nightsquad Commando in Ikoria led us to question the raid template, and we found that we had created tools that coincidentally let us shorten it. We applied this shortening to the existing cards with raid; this isn't at all a functional change since you can't attack with anything but creatures. This affects every card with a raid ability, the reminder text for melee, and Chart a Course.

Mardu Heart-Piercer was:

Raid — When Mardu Heart-Piercer enters the battlefield, if you attacked with a creature this turn, Mardu Heart-Piercer deals 2 damage to any target.

New text:

Raid — When Mardu Heart-Piercer enters the battlefield, if you attacked this turn, Mardu Heart-Piercer deals 2 damage to any target.

Activate the Shortening! (Non-Functional)

Here's another entirely stylistic change with zero functional difference—Zirda, the Dawnwaker shows off a new template for reducing costs where we don't let you hit zero. It reduces some redundant words to remove some redundancy. This change affects four cards: Training Grounds, Heartstone, Power Artifact, and Biomancer's Familiar.

Heartstone was:

Activated abilities of creatures cost {o} less to activate. This effect can't reduce the amount of mana an ability costs to activate to less than one mana.

New text:

Activated abilities of creatures cost {o} less to activate. This effect can't reduce the mana in that cost to less than one mana.

Any Clone Will Do (Non-Functional)

And one final "no, this changes nothing" change. I bring these up to reassure you that the change you see isn't functional, and this one's just cleaning up two valid templates to standardize their use. When you Clone something, sometimes we can say that you can copy "any" thing of a group, sometimes we say that you can copy "a" thing from the group. The editors decided that the line is whether there are any criteria for what you can copy; if it's just "creature on the battlefield," "any" is good. If it's a "creature you control," "any" is just "a" instead. Three cards that used "any" shifted to "a" as part of this—Mercurial Pretender, Mirror Image, and Estrid's Invocation.

Mirror Image was:

You may have Mirror Image enter the battlefield as a copy of any creature you control.

New text:

You may have Mirror Image enter the battlefield as a copy of a creature you control.

Introduction
Comprehensive Rules Changes
Oracle Changes