Iroas's Blessing — ruling 1

If the creature Iroas's Blessing would enchant is an illegal target by the time the Aura spell resolves, the entire spell doesn't resolve. It won't enter the battlefield, so its ability won't trigger.

Iroas's Blessing : règles, fonctionnement et interactions (MTG)

Iroas's Blessing 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

Enchant creature you control When this Aura enters, it deals 4 damage to target creature or planeswalker an opponent controls. Enchanted creature gets +1/+1.

How it works : Iroas's Blessing

Original English text — Wizards of the Coast / Scryfall

#1January 24, 2020· Wizards of the Coast
If the creature Iroas's Blessing would enchant is an illegal target by the time the Aura spell resolves, the entire spell doesn't resolve. It won't enter the battlefield, so its ability won't trigger.
No other card is named in this ruling.