Boss 1

Setting
The players walk along a tarn towards the mansion of the lord of Usher. A void creature emerges from this tarn. The connection to the void is not full established, and so the fight is mostly about controlling adds that spawn.

Overview
The large creature only harasses the group, as they deal with the add spawns. Larger adds need to be tanked and focused. Smaller adds need to be killed fast enough to not be overrun, but are of lower priority. The boss is damaged by killing a third add type.

Hardmode
On hardmode, a very large add needs to be dealt with. It takes 99% reduced damage. Large adds spawn a void zone upon death, which kills smaller adds. Damaging the smaller adds is thus pointless, but they can be used for funnel damage. When a large add dies, the very large add becomes vulnerable to damage. This damage is dealt to the boss as well, such that the boss dies when the very large add dies.