The Goddess mortar achievement

The achievement says "Defeat the Goddess without anyone in the party taking damage from her mortar attack." I've done this numerous times without being hit by these projectiles and still can't complete this. Is this broken or am I avoiding the wrong attack? It is the barrage of green projectiles right?

The achievement is talking about the map boss "The Goddess", from the Plaza map (the one you can sometimes fight in the Shaper's Realm also works, that's where I got it). I'm going to go ahead and assume you're talking about the Goddess that helps Izaro in the Labyrinth.

The plaza is actually one of the two zones!

You can also encounter the goddess in shaper's realm and killing her without taking damage counts too. This is usually quite easy since shaper pre-bosses have no enchantments and are fairly squishy.