It doesn't shut down anything, and it equally affects all creatures.
Once again, this affects both players, you risk yourself just as much as your opponent with this.
Except, this wouldn't be played in a deck that involved a lot of targeting, so there's really no risk. For example, I could use this barrier with a Lycanthrope + Devourer rush to basically give my Lycanthropes a ton of evasion and a good chance of getting buffed by my opponent's spells - sure, Adrenaline my Devourer! It's multiplicatively better with more creatures on your field, so it's essentially only usable in a high creature deck. If I have 4 creatures and my opponent has 2, there is a 2/3 chance a Blessing will hit my creature, making it a dead card.
To make it always advantageous for your opponent to play the Blessing (but still risky), you would need no more than 50% chance of targeting being randomized. Then there's the issue of damage spells, which could potentially backfire and kill the caster, which I won't get into now. I like the concept, but easily making a lot of cards dead cards is a bit too strong in my opinion.
