This is a summary of the rule changes planned to come to Magic with the release Dominaria United. 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

Enlist

702.154

This new section explains how the enlist mechanic works. Notable mentions include that tapping a creature for an enlist ability is an optional cost to attack (like exert), and that a creature can never enlist itself.

Read Ahead

702.155

This is the entry for read ahead, an ability found on some Saga cards that lets its controller choose how many lore counters it enters the battlefield with. A couple of minor changes to the other Saga rules were also made to accommodate this ability.

Other rules changes

111.10h

This new subrule defines a Powerstone token.

122.1d

A new rule subrule explains what stun counters mean. The rest of the rules about counters move down a spot.

301.5e

This new subrule explains what happens if an effect attempts to put an Equipment onto the battlefield attached to an object it can't legally be attached to. If that happens, it just enters the battlefield unattached (unless it's also somehow an Aura, and then it doesn't enter at all).

704.5j

This is the legend rule. There's no functional change here; we realized that, with the way it was worded, the legend rule applied to players who controlled legendary permanents rather than applying to the permanents themselves. There's nothing wrong with that in theory, except that an effect which says that the legend rule doesn't apply to certain permanents didn't make a whole lot of sense with that wording. The new wording makes the legendary permanents the subject of the rule rather than the player who controls them, which lines up with those effects much better.

715.2e

This new Saga subrule explains what the phrase "final chapter ability" means in game rules terms. Basically, it means the chapter ability with the biggest number in its chapter symbol. I imagine that most of you had probably figured that out way before reading this sentence, but the rules have to be very specific about that kind of thing.

New Subtypes

Powerstone
Sivitri

New Glossary Entries

Enlist
Powerstone token
Read ahead
Stun counter

Introduction
Comprehensive Rules Changes
Oracle Changes