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: