Hive mind allows a group of people (often biologically related) "share" the same mind. In some cases one person could take control of another separate body to add to the hive. Like most hive insects like bees and ants, each can work autonomously, though they think the same thing at the same time. The members have little individuality, more or less they are only marionettes controlled by a puppeteer.
In some cases the members of the hive mind have separate brains, mindsets, personalities, and individuality. But both are basically the same, all members work as one, they can all see, hear, and know what the others do. All work as one, each thinks with the same "mind", not as a sum of its parts.
Can be used to scout out areas being able to see and experience in multiple areas at once. If the subjects have any other powers they act as their own team or unit.
Eaters (Digimon) all operate under a single hive mind, controlled by the "Mother Eater". If one were to be separated from the hive mind, they'd start evolving beyond any and all control.
Mother Eater (Digimon) regulates the Eater Hive mind, and makes sure that all assimilated data is shared equally amongst all units.
Zazzala (DC Comics) is the queen of a race of bee-like aliens and controls their hive-mind.
The Parliament of Trees (DC Comics) have given up everyday speech and mobility, communicating through one unified mind.
The Aurum Brain (Kid Icarus: Uprising) is the hive mind behind the Aurum race.
Ultron Sentries (Marvel Cinematic Universe) act as a extension of Ultron himself.
Krakoa's (Marvel Comics) entire ecosystem operates under a hive mind.
Stepford Cuckoos (Marvel Comics)
Nagato (Naruto), who controls his Six Paths of Pain.
Obito Uchiha (Naruto) creates his own Six Paths of Pain using the reincarnated jinchūriki…
…which share the same vision Rinnegan and mind of each one simultaneously.
Elizabeth Greene (Prototype) and her legions of Infected.
Alex Mercer (Prototype) tapping into the Infected hive mind.
Beta-7 (left-far left) & Unity (far right) (Rick and Morty) are two variations of a hive-mind.
Million Ants (Rick and Morty) is made of multiple ants.
Lazarus 92 (Samurai Jack) is made of multiple poisonous leeches.
Dionysus (The Wicked + The Divine) is able to allow others into his collective hive-mind
The Lord of Dust (Metal Gear Survive) is the central focus of the Dread Dust hive mind and its byproducts, including the Wanderers.
The Gravemind (Halo) is the hive mind of the entire Flood species, connected to ever single Flood cell in existence.
Kraang Prime (Teenage Mutant Ninja Turtles 2012) telepathically enslaved many Utroms…
…turning them into a hive-minded collective calling themselves the Kraang.
Those enslaved to Jasmine's (Angel) mind control become extensions of her mind and body...
...part of the Body Jasmine.
The Black Arms (Sonic the Hedgehog) all follow a hive mind under the command of their leader Black Doom.
Black Death (Archie's Sonic the Hedgehog) now controls the Black Arms' hive mind after the death of Black Doom.
Eclipse the Darkling (Archie's Sonic the Hedgehog) using the Black Arms' hive mind...
...to communicate with Shadow.
Shadow the Hedgehog (Archie's Sonic the Hedgehog) tapping into the Black Arms hive mind.
The Nanochips (Ben 10) are hive-minded robotic insects that follow a queen.
Elena Validus (Ben 10) is the current queen of the Nanochips.
The Sisters (A Certain Magical Index) are linked together.
The Will of the Whole Misaka Network (A Certain Magical Index) is a thought entity, created from the gathering and consciousness and egos of the Sisters, due to this she is a hive mind of all the Sisters.
The Unown (Pokemon)
Kai (Kung Fu Panda)
Toothiana (Rise of the Guardians) is able to separate herself into mini versions of herself called the...
...Mini-Fairies that are extensions of Tooth herself, that she can split herself into smaller copies, and she is mentally connected to all of them.
Horde Prime's (She-Ra and the Princesses of Power) hive mind allows him to control his clones and can link others to it using Horde chips.
Rom, The Vacuous Spider (Bloodborne), protects himself with his minions who attack together making a seemingly easy boss fight more strategic.