Master Symmetrist — ruling 1

Master Symmetrist’s triggered ability only looks at the power and toughness of a creature when it attacks. Once the ability has triggered, changing the creature’s power or toughness will not stop it from gaining trample or remove trample from it.

Master Symmetrist : règles, fonctionnement et interactions (MTG)

Master Symmetrist 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

Reach Whenever a creature you control with power equal to its toughness attacks, it gains trample until end of turn.

How it works : Master Symmetrist

Original English text — Wizards of the Coast / Scryfall

#1April 16, 2021· Wizards of the Coast
Master Symmetrist’s triggered ability only looks at the power and toughness of a creature when it attacks. Once the ability has triggered, changing the creature’s power or toughness will not stop it from gaining trample or remove trample from it.
No other card is named in this ruling.