Librarian

Librarians are enemies found in the Astrolab, wearing a yellow hood that covers their face. They ride on top of a large magical book, floating around in the air. They are exclusive to the Rise of the Giant DLC.

Behavior
Upon spotting the Beheaded, it will fly directly above the player and use its beam attack. After attacking three times, it will circle around the player counterclockwise before it can attack again.

Strategy
Librarians are like an even worse version of Bombers. Their detection range isn't as large, but once they are aggroed, they will immediately fly into position above you and out of reach from most attacks. They have perfect tracking and are nearly impossible to run away from. Even with a speed boost buff, the layout of Astrolab leaves you with very little room to sprint away. Shields are useless against them so rolling is your only option.

You should kill a Librarian before they even get to attack whenever possible. Use your burst damage or crowd control skills to make sure they don't even get to start flying up. If you lack these options, you should at the very least lure our any nearby enemies and fight the Librarian solo so you can focus completely on dodging just the Librarian's beams. Whatever you do, never fight it with multiple enemies if you can't kill them fast enough.

Anything that hits in a large radius like Lacerating Aura or Tesla Coil are very effective against Librarians. Some weapons with a high vertical hitbox can hit Librarians even if they are above you, such as the second and third hits of Rhythm n' Bouzouki and the first hit of Flawless.

Magic Missiles are very effective against this enemy, being able to hit them virtually anywhere.

The Pure Nail is also a useful weapon against Librarians. If a Librarian is above you, jump and quickly attack upwards using the weapon to quickly defeat them.

Trivia

 * Librarians were added with the v1.4 update, aka Who's the Boss Update in August 2019 as an enemy deriving from the fourth boss.