Psion
Psion is a psionic mini-boss found within 
Sheol.
Behavior
Psion will manifest in the center of the room, and while there are any other enemies are alive, it will bounce around the room diagonally with a barrier that grants it invulnerability. Once all other enemies in the room are killed, it will remove the barrier and perform one of two attacks:
- Summons 4 large purple projectiles in a plus pattern around itself which all simultaneously fire
Technology lasers at Isaac's position, of which the lasers will be telegraphed by purple beams. Psion will perform this attack twice in a row. - Summons 4 large purple projectiles to Psion's left and right sides, which begin to travel towards Isaac one at a time. Each projectile will stop in place after traveling a certain distance, and then redirect themselves towards Isaac once more.
After Psion has finished attacking, it will spawn a single Psionic enemy and then grant itself a new barrier until the spawned enemy is killed, repeating the cycle until Psion is killed.
The enemies Psion can directly spawn are as follows:
Upon being defeated in the Sheol Mini-Boss Room, Psion will drop one of the following:
- An item from the
Devil Deal item pool. - A
Black Heart.
Video Showcase
Unlockable Achievements
Trivia
- Psion and its underlings are inspired by Beholders from the Dungeons and Dragons tabletop RPG series.
- HappyHead, one of the developers, made the sounds for Psion.
- Psion in Isaac's Last Will, seems to resemble it's earlier design moreso than it's current one.
Gallery
Psion when performing its psychic projectile attack.
Psion when performing its psychic laser attack.
Drawing of Psion in the Bestiary and on Isaac's last will.
Psion's health bar icon if Enhanced Boss Bars is installed.
An older sprite of Psion.
 Bosses 
| |
|---|---|
| Chapter 1 | Buck - Honeydrop - The Whispers - Griddle Horn - Buster - Meltdown |
| Chapter 1.5 | Ghostbuster - Cacamancer |
| Chapter 2 | Battie - Kingpin - Slinger - Monsoon - Aquagob |
| Chapter 3 | The Organization - Gutso the Great - Luncheon - Pollution - Tsar - Junkstrap |
| Chapter 3.5 | Warp Zone - Dusk - Madomme |
| Chapter 4 | Basco - The Sun - Peeping - Cacophobia |
| Chapter 4.5 | Mr. Dead |
| Minibosses | Psion - Gravedigger - Hermit |
| Vanilla Boss Champions | Golden Plum - Ghost Larry Jr. - Mucus Monstro - Technopin - Albino Widow - Beehive Fistula - Possessed Hollow - Wine Husk - Kidney of Infamy - Alien Loki - Fiend Mom - Alien Lokii - Grinch Krampus |