This is a summary of the rules changes planned for Magic with the release of Innistrad: Crimson Vow. The official rules are still under review at the time of this writing. When they are published, they can be found on our rules page. If there should be a discrepancy between this summary and the official rules, the official rules take precedence.
New and Updated rules
According to this rule, if a spell or ability created a token without specifying its name, the token's name was the same as its subtypes. For example, an effect which says "create a 2/2 Illusion creature token" would create a token whose name was Illusion. This had some uncommon but weird interactions with effects that let you choose the name of a card, such as those of Pithing Needle and Runed Halo. Since you can only choose names of printed cards for such effects, you usually can't choose the name of a token. Sometimes, however, the name of an unrelated card happens to overlap with the name of a token, such as the Illusion half of the split card Illusion // Reality. In that case, choosing the name of the card would apply any relevant effects to tokens named Illusion.
With the creation of Blood tokens in Innistrad: Crimson Vow, this relatively obscure interaction had the potential to become significantly more common (see Flesh // Blood). The fact that a player could stop Blood tokens with Pithing Needle's effect but not Treasure, Food, or Clue tokens is inconsistent, and players shouldn't be expected to know which tokens share a name with a printed card, so we decided to change the rule. From now on, if a spell or ability is creating a token without specifying its name, the name will be the same as its subtypes plus the word "Token." For example, a "Goblin Scout creature token" is named "Goblin Scout Token." Similarly, the name of a Blood token created in the game is "Blood Token" and choosing the name "Blood" for an effect will not cause that effect to apply to Blood tokens.
Note that Blood token supplements found in Innistrad: Crimson Vow boosters will only have the word Blood on the name line. This does not affect gameplay. Also keep in mind that this rule change does not apply to a token that is a copy of another permanent or was created due to an ability that specified its name, such as that of Llanowar Mentor.
This rule adds Blood tokens to the list of predefined tokens.
This rule adds Blood to the list of artifact types.
The rule that covered secondary title bars for some versions of Ikoria: Lair of Behemoths cards has been generalized and expanded to make sure it includes cards from the Innistrad: Crimson Vow set and any future card with a secondary title bar and an alternate name.
Day/Night and Daybound/Nightbound
Day/night didn't mention that it was a turn-based action in all the appropriate places. Now it is properly referenced in each place it should be.
New Keyword Abilities
702.148 is the new rule that defines the cleave mechanic.
702.149 is the new rule that defines the training mechanic.
New Glossary Entries
Alternate name, Blood token, cleave, flavor word, secondary title bar, training