I know I knew this once, but it's been so long, so forgive my inquiry. Does Bard's ability take effect as soon as the attack is declared, or after it is resolved? Given the writing of the news article, I'm thinking it takes effect after it is resolved. I'm assuming the same thing would happen for other abilities that lower defense or attack of a target after attacking it (though I can't think of other examples at the moment).

But if it takes effect after it resolves, it wouldn't be of any use for Bard !!

Guess it only makes sense if it takes effect at the start.

Bard the Bowman:
When Bard the Bowman makes a ranged attack …

It is the same wording on the errata'd Dol Guldur Beastmaster, so it will take effect when it is declared as an attacker using range attack.