Basri, Devoted Paladin — ruling 1

After activating Basri's second ability, a creature that attacks gets a +1/+1 counter before blockers are chosen.

Basri, Devoted Paladin — ruling 2

Basri's last ability affects only creatures you control at the time it resolves. Creatures you begin to control later in the turn won't get +2/+2 or gain flying.

Basri, Devoted Paladin : règles, fonctionnement et interactions (MTG)

Basri, Devoted Paladin 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

+1: Put a +1/+1 counter on up to one target creature. It gains vigilance until end of turn. −1: Whenever a creature attacks this turn, put a +1/+1 counter on it. −6: Creatures you control get +2/+2 and gain flying until end of turn.

How it works : Basri, Devoted Paladin

Original English text — Wizards of the Coast / Scryfall

#1June 23, 2020· Wizards of the Coast
After activating Basri's second ability, a creature that attacks gets a +1/+1 counter before blockers are chosen.
No other card is named in this ruling.
#2June 23, 2020· Wizards of the Coast
Basri's last ability affects only creatures you control at the time it resolves. Creatures you begin to control later in the turn won't get +2/+2 or gain flying.
No other card is named in this ruling.

Interactions with other cards

These cards' text mentions Basri, Devoted Paladin.

Basri's Aegis

Put a +1/+1 counter on each of up to two target creatures. You may search your library and/or graveyard for a card named Basri, Devoted Paladin, reveal it, and put it into your hand. If you search your library this way, shuffle.