Fluros of Myra's Marvels — ruling 1

Fluros’s middle ability triggers only once if you cast a creature or Vehicle spell with power and toughness both equal to the chosen number.

Fluros of Myra's Marvels — ruling 2

Fluros’s middle ability will overwrite any previous effects that set the target’s power and toughness (if any) to specific numbers. Effects that otherwise modify its power and toughness will still apply no matter when they took effect. The same is true for +1/+1 counters.

Fluros of Myra's Marvels — ruling 3

If Fluros’s middle ability causes a Vehicle to become an artifact creature, it doesn’t count as “crewing” that Vehicle for any ability that would trigger off of a Vehicle becoming crewed. That Vehicle will become an X/X artifact creature, not whatever its printed power/toughness is.

Fluros of Myra's Marvels — ruling 4

Even in an Un- game, you must choose 0 or a positive integer. This is a change from previous Un- rules.

Fluros of Myra's Marvels : règles, fonctionnement et interactions (MTG)

Fluros of Myra's Marvels 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

As Fluros of Myra's Marvels enters, choose a number greater than 0. Whenever you cast a spell with power, toughness, or loyalty equal to the chosen number, target artifact or creature becomes an artifact creature with base power and toughness X/X until end of turn, where X is the chosen number. Partner

How it works : Fluros of Myra's Marvels

Original English text — Wizards of the Coast / Scryfall

#1October 7, 2022· Wizards of the Coast
Fluros’s middle ability triggers only once if you cast a creature or Vehicle spell with power and toughness both equal to the chosen number.
No other card is named in this ruling.
#2October 7, 2022· Wizards of the Coast
Fluros’s middle ability will overwrite any previous effects that set the target’s power and toughness (if any) to specific numbers. Effects that otherwise modify its power and toughness will still apply no matter when they took effect. The same is true for +1/+1 counters.
No other card is named in this ruling.
#3October 7, 2022· Wizards of the Coast
If Fluros’s middle ability causes a Vehicle to become an artifact creature, it doesn’t count as “crewing” that Vehicle for any ability that would trigger off of a Vehicle becoming crewed. That Vehicle will become an X/X artifact creature, not whatever its printed power/toughness is.
No other card is named in this ruling.
#4October 7, 2022· Wizards of the Coast
Even in an Un- game, you must choose 0 or a positive integer. This is a change from previous Un- rules.
No other card is named in this ruling.