Formerly separate creatures pulled into an already existing body

• Flowey/ Asriel Dreemurr he/him and human/monster SOULs

  • Asriel Dreemurr and Chara's SOUL.
  • Flowey and the six dead human SOULs in the Photoshop Flowey fight
  • Asriel Dreemurr, all monsterkind and the six dead human SOULs as God of Hyperdeath

• GLaDOS she/her (Portal)

  Comprised of Aperture Science Personality Constructs, also Personality Cores or Personality Spheres

  • GLaDOS (the machine)
    • GLaDOS (the person) she/her (host)
    • Caroline she/her (likely) until the end of Portal 2. Not known about in Portal 1 but canonically present. Originally uploaded into the machine but treated as a separate entity by GLaDOS (the person)
  • Pre-Portal - Wheatley he/him
  • Portal 1 - Morality Core, Curiosity Core, Knowledge Core, Emotion Core
  • Portal 2 - Space Core, Adventure Core (Rick), Fact Core

• Kirby (Kirby franchise)
• Samuel Hayden & VEGA (DOOM)
• V & Johnny Silverhand (Cyberpunk 2077)
• The Stitchwraith (Fazbear Frights 1: Into the Pit)

Formerly separate creatures combining into a new body that's created during the process

• Akemi Homura (Puella Magi Madoka Magica)
• Amalgamates (Undertale)
• Bill (Void Entity) it? (Hollow knight)
• Moon Knight (Moon Knight)
• Ennard (Five Nights at Freddy's: Sister Location)

Creatures that have always shared a body

• Sun, Moon & Eclipse (Five Nights at Freddy's: Security Breach - Ruin)

Hivemind

• The Hive (Hollow Knight)
• The Radicance (Hollow Knight)
• Vortigaunts (Hλlf-Life)

Mixed type/origin

• The Doctor (Doctor Who)

Uncertain

• possibly Frisk & Chara (Undertale)

Unknown origin

Unsorted

• Master Chief & Cortana (Halo)
• Cortana (Halo)
• Raven (Teen Titans)
• The Avatar (ATLA & TLoK)
• Entities (Worm)
• Syler/Gabriel Gray (Heroes)
• Niki Sanders (Heroes)
• Peter Petrelli (Heroes)
• Protag (Persona Franchise)
• Protag (Talos Principle)
• Crystal Gems (Steven Universe)
• Devourer of Worlds joke? (Terraria)
• Courier & Stealth Suit MKII (Fallout: New Vegas)
• August 8th Cluster (Sense8)
• Clones (Orphan Black)
• Midoriya Izuku (My Hero Academia)
• Toga Himiko (My Hero Academia)
• Twice (My Hero Academia)
• The Gods (PJO/HOO)
• Harry DuBois (Disco Elysium)
• Sakura Haruno (Naruto)
• Lain Iwakura (Serial Experiments Lain)
• Rumi Hidaka (Perfect Blue)
• Mima Kirigoe (Perfect Blue)

Credits.

• Crystal Cluster - Portal.
• Serenity Amalgam - ATLA & TLoK, Cyberpunk 2077, Doctor Who, DOOM, Fallout: New Vegas, Geometry Dash, Hλlf-Life, Halo, Heroes, Kirby, Moon Knight, Teen Titans, Persona, Puella Magi Madoka Magica, Steven Universe, Terraria, The Talos Principle, Undertale.
• Arelia - FNAF