Mystic Subdual — ruling 1

If the affected creature gains an ability after Mystic Subdual becomes attached to it, it will keep that ability.

Mystic Subdual — ruling 2

If a creature has power and toughness written as */* with an ability that defines its power and toughness, its base power and toughness become 0/0 when it loses all abilities. Mystic Subdual then makes it a -2/0. If its power and toughness are written as */*+1, it’s -2/1, and so on.

Mystic Subdual — ruling 3

Mutating the enchanted creature won’t cause it to gain abilities. This is because mutate modifies the creature’s base characteristics, while Mystic Subdual applies to the resulting creature.

Mystic Subdual : règles, fonctionnement et interactions (MTG)

Mystic Subdual 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

Flash Enchant creature Enchanted creature gets -2/-0 and loses all abilities. (Mutating onto the creature won't give it new abilities. It can gain abilities in other ways.)

How it works : Mystic Subdual

Original English text — Wizards of the Coast / Scryfall

#1April 17, 2020· Wizards of the Coast
If the affected creature gains an ability after Mystic Subdual becomes attached to it, it will keep that ability.
No other card is named in this ruling.
#2April 17, 2020· Wizards of the Coast
If a creature has power and toughness written as */* with an ability that defines its power and toughness, its base power and toughness become 0/0 when it loses all abilities. Mystic Subdual then makes it a -2/0. If its power and toughness are written as */*+1, it’s -2/1, and so on.
No other card is named in this ruling.
#3April 17, 2020· Wizards of the Coast
Mutating the enchanted creature won’t cause it to gain abilities. This is because mutate modifies the creature’s base characteristics, while Mystic Subdual applies to the resulting creature.
No other card is named in this ruling.