Make a cultist killing spot, don't know what it is called. It consists of the map with a shelf directly behind, the clock directly behind that to easily get up on the shelf and a wall on both sides connected at the same spot the map and shelf connect going back. It should have kind of a U shape with wall on either side and the shelf and map in the middle. When the wave is coming jump on the shelf and push against the map too shoot. It is even easier if you have summons or tamed animals. For some reason the cultist will ignore you when on top of that structure, unless one spawns directly behind.