Bria, Riptide Rogue — ruling 1

Once a prowess ability triggers, causing the creature to lose prowess by removing Bria from the battlefield won’t affect that ability. The creature will still get +1/+1 until end of turn.

Bria, Riptide Rogue — ruling 2

Bria’s last ability resolves before the spell that caused it to trigger. It resolves even if that spell is countered.

Bria, Riptide Rogue : règles, fonctionnement et interactions (MTG)

Bria, Riptide Rogue 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

Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.) Other creatures you control have prowess. (If a creature has multiple instances of prowess, each triggers separately.) Whenever you cast a noncreature spell, target creature you control can't be blocked this turn.

How it works : Bria, Riptide Rogue

Original English text — Wizards of the Coast / Scryfall

#1July 26, 2024· Wizards of the Coast
Once a prowess ability triggers, causing the creature to lose prowess by removing Bria from the battlefield won’t affect that ability. The creature will still get +1/+1 until end of turn.
No other card is named in this ruling.
#2July 26, 2024· Wizards of the Coast
Bria’s last ability resolves before the spell that caused it to trigger. It resolves even if that spell is countered.
No other card is named in this ruling.