Basri's Aegis — ruling 1

You can cast Basri's Aegis without any target creatures. You'll just search for Basri, Devoted Paladin.

Basri's Aegis — ruling 2

If do you choose targets and each target creature is an illegal target by the time Basri's Aegis tries to resolve, the spell won't resolve. You won't search for Basri. If just one target is still legal, however, you do put a +1/+1 counter on it and search for Basri.

Basri's Aegis : règles, fonctionnement et interactions (MTG)

Basri's Aegis 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

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.

How it works : Basri's Aegis

Original English text — Wizards of the Coast / Scryfall

#1June 23, 2020· Wizards of the Coast
You can cast Basri's Aegis without any target creatures. You'll just search for Basri, Devoted Paladin.
Card named in this ruling
Basri, Devoted Paladin
#2June 23, 2020· Wizards of the Coast
If do you choose targets and each target creature is an illegal target by the time Basri's Aegis tries to resolve, the spell won't resolve. You won't search for Basri. If just one target is still legal, however, you do put a +1/+1 counter on it and search for Basri.
No other card is named in this ruling.