Mu Yanling, Celestial Wind — ruling 1

Mu Yanling’s last ability affects only creatures you control with flying at the time it resolves. Creatures you begin to control later in the turn (or creatures that that gain flying later in the turn) won’t get +5/+5.

Mu Yanling, Celestial Wind — ruling 2

In a multiplayer game, if you leave the game after Mu Yanling’s first ability resolves but before your next turn begins, its effect lasts until your next turn would have begun. It neither expires immediately nor lasts indefinitely.

Mu Yanling, Celestial Wind : règles, fonctionnement et interactions (MTG)

Mu Yanling, Celestial Wind 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

+1: Until your next turn, up to one target creature gets -5/-0. −3: Return up to two target creatures to their owners' hands. −7: Creatures you control with flying get +5/+5 until end of turn.

How it works : Mu Yanling, Celestial Wind

Original English text — Wizards of the Coast / Scryfall

#1July 12, 2019· Wizards of the Coast
Mu Yanling’s last ability affects only creatures you control with flying at the time it resolves. Creatures you begin to control later in the turn (or creatures that that gain flying later in the turn) won’t get +5/+5.
No other card is named in this ruling.
#2July 12, 2019· Wizards of the Coast
In a multiplayer game, if you leave the game after Mu Yanling’s first ability resolves but before your next turn begins, its effect lasts until your next turn would have begun. It neither expires immediately nor lasts indefinitely.
No other card is named in this ruling.

Interactions with other cards

These cards' text mentions Mu Yanling, Celestial Wind.

Yanling's Harbinger

Flying When this creature enters, you may search your library and/or graveyard for a card named Mu Yanling, Celestial Wind, reveal it, and put it into your hand. If you search your library this way, shuffle.