@JeremyECrawford A Goblin is hidden in a bush, it attacks & then uses it's BA to re-hide. Do I now know where it is & can it be targeted?
— ubergrog (@ubergrog) February 24, 2017
In that scenario, you guess where the goblin is (your guess is right), and you'll attack with disadvantage because you can't see it. #DnD https://t.co/LfR5usvgxG
— Jeremy Crawford (@JeremyECrawford) February 24, 2017
Fireball? Vicious Mockery?
Vicious Mockery requires that you see your target.
Nothing stops you from burning the bush to the ground with a fireball though.