Majestic Myriarch — ruling 1

If one of those creatures has one or more variants of the listed keywords (for example, hexproof from white), this creature gains those specific variants.

Majestic Myriarch — ruling 2

Majestic Myriarch's first ability applies in all zones. While it's on the battlefield, it counts itself, so it'll be at least 2/2.

Majestic Myriarch — ruling 3

Majestic Myriarch's second ability triggers at the beginning of each combat, not just combat on your turn, whether or not any creatures you control have any of the listed abilities.

Majestic Myriarch — ruling 4

Which abilities Majestic Myriarch gains is determined as the ability resolves. They won't change even if every other creature that has the abilities leaves the battlefield or if creatures enter the battlefield or gain abilities.

Majestic Myriarch — ruling 5

If a creature gains one of the listed abilities before Majestic Mryiarch's triggered ability resolves, perhaps due to another ability that triggered at the beginning of combat, Majestic Myriarch will gain that ability.

Majestic Myriarch — ruling 6

Multiple instances of any of the abilities Majestic Myriarch can gain are redundant.

Majestic Myriarch : règles, fonctionnement et interactions (MTG)

Majestic Myriarch is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Majestic Myriarch's power and toughness are each equal to twice the number of creatures you control. At the beginning of each combat, this creature gains flying until end of turn if you control a creature with flying. The same is true for first strike, double strike, deathtouch, haste, hexproof, indestructible, lifelink, menace, reach, trample, and vigilance.

How it works : Majestic Myriarch

Original English text — Wizards of the Coast / Scryfall

#1January 24, 2020· Wizards of the Coast
If one of those creatures has one or more variants of the listed keywords (for example, hexproof from white), this creature gains those specific variants.
No other card is named in this ruling.
#2July 14, 2017· Wizards of the Coast
Majestic Myriarch's first ability applies in all zones. While it's on the battlefield, it counts itself, so it'll be at least 2/2.
No other card is named in this ruling.
#3July 14, 2017· Wizards of the Coast
Majestic Myriarch's second ability triggers at the beginning of each combat, not just combat on your turn, whether or not any creatures you control have any of the listed abilities.
No other card is named in this ruling.
#4July 14, 2017· Wizards of the Coast
Which abilities Majestic Myriarch gains is determined as the ability resolves. They won't change even if every other creature that has the abilities leaves the battlefield or if creatures enter the battlefield or gain abilities.
No other card is named in this ruling.
#5July 14, 2017· Wizards of the Coast
If a creature gains one of the listed abilities before Majestic Mryiarch's triggered ability resolves, perhaps due to another ability that triggered at the beginning of combat, Majestic Myriarch will gain that ability.
No other card is named in this ruling.
#6July 14, 2017· Wizards of the Coast
Multiple instances of any of the abilities Majestic Myriarch can gain are redundant.
No other card is named in this ruling.