As  was playing one of the Hidden Depths DLC missions, I came across a drowned necromancer, and figured, Why not try and get the "Gone Fishin'" achievement. After making multiple attempts to hook the drowned necromancer, I found it was impossible. Part of the problem is probably how often the necromancer summons the drowned. As soon as they're gone, I try aiming directly at the necromancer, and it passes straight through him. And as soon as the drowned are killed, three more are summoned.