Priority Avenger — ruling 1

Among abilities, only activated and triggered abilities use the stack. Activated abilities are written in the form “[Cost]: [Effect].” Triggered abilities use the word “when,” “whenever,” or “at.” They’re often written as “[Trigger condition], [effect].” Some keyword abilities are activated abilities and will have colons in their reminder texts, and some keyword abilities are triggered abilities and will have “when,” “whenever,” or “at” in their reminder texts.

Priority Avenger — ruling 2

Non-instant spells with flash may still be cast any time a player has priority, regardless of what’s on the stack. The same is true of activating abilities.

Priority Avenger : règles, fonctionnement et interactions (MTG)

Priority Avenger 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

Flying Players can't cast instant spells unless a spell or ability is on the stack.

How it works : Priority Avenger

Original English text — Wizards of the Coast / Scryfall

#1November 12, 2019· Wizards of the Coast
Among abilities, only activated and triggered abilities use the stack. Activated abilities are written in the form “[Cost]: [Effect].” Triggered abilities use the word “when,” “whenever,” or “at.” They’re often written as “[Trigger condition], [effect].” Some keyword abilities are activated abilities and will have colons in their reminder texts, and some keyword abilities are triggered abilities and will have “when,” “whenever,” or “at” in their reminder texts.
No other card is named in this ruling.
#2November 12, 2019· Wizards of the Coast
Non-instant spells with flash may still be cast any time a player has priority, regardless of what’s on the stack. The same is true of activating abilities.
No other card is named in this ruling.