Shadow Assassin

The Shadow Assassin is a in The Catacombs that appears from Floor 3 onward.

Spawning
Shadow Assassins spawn as Mini-Bosses in The Catacombs on Floor 3 and above. Their health and damage scales by their floor and dungeon progress; if spawned in a yellow room, it is significantly buffed.

Necron fight
4 Shadow Assassins spawn in each corner of the arena during the 2nd phase of Necron‘s fight. They have each.

Behavior
The Shadow Assassin can teleport and is extremely agile. It has the highest melee damage of any mini-boss and does additional damage when attacking from behind. However, it does not have a healing ability.

Unlike the Lost Adventurer and Angry Archaeologist, this mob counts as an undead mob; thus, additional damage from the Dark, Shadow and Wither Goggles applies.

Necron fight
The Shadow Assassins protect the four control pads for the crushers at the four corners of the room. Necron will try to protect them, attacking any player who attacks them.

Trivia

 * Shadow Assassins could have been Livid's shadows that Livid mentioned when he was about to perish.
 * This is further suggested since they have an emblem on their body very similar to the emblem in Livid's room.
 * In the quote, it suggests that the Shadow Assassin's name might be Albert, or it could be that the person talking was protecting someone of the name, Albert, from the Shadow Assassin.
 * In The Catacombs (Master Mode), Shadow Assassins may spawn an upwards of 150M health in M5.