DarkErr

"The hidden mechanical menace of the darkened lands"

The DarkErr is a post - mech boss that spawns if the player waits long enough in the underground darkness biome. The boss is quite resilient, but has a relatively low amount of health. It can also be spawned with the "pure darkness" summoning item. It can easily decimate an unprepared player, and like most bosses, is mechanical.

Stage one:
Will fire a thin, yet damaging stream of cursed flames. The cursed flames are similar to spartsazam's second form, although have a shorter range and is much more damaging.

Will also spawn two random minions every 25% health. The minions follow the bat AI, and will randomly fly towards the player. The minions are quite powerful, and can swarm a player who does not have crowd control.

Stage two:
The eye will turn red, and the mouth will open. The boss will fire a much bigger stream of cursed flames that are harder to dodge.

Gains the ability to ram at the player, dealing a considerable amount of damage, although all other attacks will stop when ramming.

Will spawn three minions at every 15% health.

Will also fire ichor lasers every couple of seconds.

Expert:
In expert mode, the first stage is similar to normal mode's, but the boss is slightly more damaging.

In the second form, the cursed stream instead inflicts the far more damaging Ichorflames, and won't stop the other attacks when ramming, meaning that dodging is a necessity.