Minions

Souls
These are minions that can perform several things such as attack enemies, and provide stat boosts to bullets passing through them. These cannot be killed.

Figments
Figments act like Souls, minions that help you out but can be attacked and can die. They respawn after each room. After a recent update, they now do 5 contact damage to bosses.

Trivia

 * Souls used to get stuck in walls
 * Clingy Soul used to vibrate rapidly back and forth in a wall
 * Electro Soul currently breaks melee weapons with correct timing
 * Electro Soul also breaks melee weapons when fired into the wall
 * Figments only recently got contact damage
 * Figments were at one point incapable of dying from boss contact
 * The boss Manifest Core has transparency that allows it to seemingly carry figments around, when in reality the figments are following it
 * Figments wall collision used to be busted
 * Figments were capable of being stuck in walls
 * Eye Sore was capable of running straight off out of bounds
 * Bosses like Cursed Clappers were able to push figments out of bounds, soft-locked the game with the other glitch where figments couldn't die from boss contact
 * Thought figments used to suck up projectiles but there were complaints
 * Thought figments thoughts were able to be slingshotted out of bounds via soul movement
 * Blaze Soul and Poison Soul used to break many sprites
 * Beams do not work with damage over time souls
 * Twister Staff and Blaze Soul used to break
 * Fuse Soul and beam weapons make explosions at the base of the soul
 * Fuse Soul used to display NaN damage counts occasionally
 * Electro Soul used to crash the game
 * Electro Soul used to remove extra hit from projectiles
 * Magician Soul used to break Boss Munchers
 * Warding Fig and Bullet Eater used to be able to move acid pools, Wall Watcher champ laser beams, etc.
 * Dummy Figment had broken move code earlier in the game
 * Explosive Manifesto doesn't do explosion damage
 * Copy Cat Soul used to not function correctly with charge weapons
 * Copy Cat Soul can go out of bounds, causing weird things to happen with Space Bender
 * Troubling Thingo and Space Bender kills you (pretty much)
 * Copy Cat Soul has 0 weapon delay with charge weapons, pretty broken
 * There's probably more old glitches I forgot and all of these are only from demo 4 until now