Enchant creature you control
When Iroas’s Blessing enters, it deals 4 damage to target creature or planeswalker an opponent controls.
Enchanted creature gets +1/+1.
The blessing is not the strength itself, but the knowledge of how to use it.
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.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.