Characters

There are 6 Characters as of now.

Null
The default normal mode.
 * The Twelfth Visitor
 * UNLOCK: Unlocked by Default

D-13
The default hard mode.
 * The Thirteenth Visitor
 * UNLOCK: Defeat The Machine as Null

Overlord
Uses only Swords. Default Weapon is also Sword
 * Sword mode
 * UNLOCK: Kleines' Shop after defeating Monolith as D-13

???
Each room has a pre-determined weapon. If ??? runs out of ammo, its weapons will lose keywords effects until ammo is replenished.
 * Chaos Mode
 * Weapon Terminals doesn't drop any weapons, but instead drops a Heart and 50% Ammo refill, but you can only choose one; also drops a Vault Key if there is a Key door Vault room in the floor
 * UNLOCK: Kleines' Shop after defeating The Machine or Monolith (Hard Mode) as Overlord

Skully
Every weapon Skully equips will 'fuse' with its own weapon, Skully. If Skully runs out of ammo, its weapon becomes its default weapon and lose the fused effects until ammo is replenished.
 * Modular Weapons
 * After defeating a boss, an 50% ammo refill will appear instead of a 5% Damage increase.
 * UNLOCK: Currently Unknown
 * Skully is just called 'visitor' by Database
 * The Artifact Upgrade can't appear when playing as Skully

Arena Blaster
A. Blaster doesn't use bombs and instead uses active skills with charges; also, to open secret rooms, you have to use 2 charges.
 * No bombs use active skills
 * Bombs don't spawn when playing as A. Blaster.
 * Floors have a Skill Terminal room that you can use to change your active skill.
 * UNLOCK: Kleines' Shop after beating the game as Skully
 * A. Blaster is the 10th visitor according to Database
 * An upgrade exclusive to A. Blaster appears when playing as it, called Capacity

Differences between characters

 * If D-13 beats The Machine in normal mode, it will enter the final Upgrade Terminal instead of destroying it.
 * If Null or Skully goes to fight Monolith, Eternal Null will have ?? on it.
 * Overlord has a mask when confronting it as Overlord.
 * ??? has a unique scene after defeating The Machine.
 * If D-13 faces himself on the boss mirror, he will have ?? on it.