The Cultist is a child of the Gungeon[1], implied to have been born there. It is suggested that they may wish to obtain the Gun That Can Kill The Past so that an (otherwise unmentioned) sibling takes the blame for spilling grape juice on a couch[2], however this is never mentioned outside of a hypothetical.
Over the course of accompanying another Gungeoneer through the Gungeon, they slowly grow jealous of the protagonists importance, and are mistreated and demeaned by various NPCs. Eventually, The Cultist decides that they will defeat player one, and take their place in the role of protagonist.
Past Kill
If The Gun That Can Kill The Past is used on The Cultist, they will be brought back to The Breach earlier that same day. The Cultist will tell the protagonist that they are sick of being referred to as "Number 2" and will then challenge them to a duel over who the game's story will focus on. Two pedestals each carrying a Magnum will have spawned, one behind the protagonist and one behind The Cultist. The two players are then allowed to move around The Breach, pick up a Magnum and fight each other to the death. Each player has 3 hearts and 2 blanks. The Breach is completely devoid of any of the usual NPCs at this time and all doorways, including the entrance to the Gungeon, are blocked off. A few tables are also scattered around, as to provide cover during the fight. If The Cultist wins the duel, they declare themself the hero only to realize that their actions could very well make them the villain.
Regardless of who wins the duel, the Cultist's alternate costume will be unlocked.
Like all characters in Exit the Gungeon, the Cultist's escape route up through the Gungeon features a series of unique elevators.
The Forge
The Hollow
Black Powder Mine
Gungeon Proper
Keep of the Lead Lord
Six individual two-layer platforms each carried by a balloon. Falling Arrowkin will periodically pop these balloons and cause the platform to fall until the balloon respawns.
Standard two-level elevator with additional higher platforms. Periodically, a skull will appear and fire a wave of arrows which must be avoided.
A horizontal sidescroller in which the player must navigate through several obstacles while a mechanical wall of sawblades chases them. Touching the sawblades deals damage.
No elevator. The player must climb a series of rickety platforms to keep pace with an auto-scrolling camera.
Same for all characters. A free-moving rocket powered platform which bounces around the elevator shaft.
Notes
NPCs in The Breach and the Gungeon shopkeepers will refuse to talk to The Cultist, declaring that they will only speak to the protagonist. Some will even insult The Cultist by pointing out their young age or the low quality of their starting weapon.
If either player has stolen something, in the Cultist's past, the Cultist may refer to the main character as "thief". This may be a reference to The Legend of Zelda: Link's Awakening.
When entering another Gungeoneer's past, the Cultist will usually only have a Dart Gun. The exceptions to this are the Bullets Past, where the Cultist begins with nothing and will gain a duplicate Wooden Blasphemy at the same time as the Bullet, and the Pilot's Past, where the cultist appears as a purple copy of the Pilot's spaceship.
In the timefall sequence after using the Gun That Can Kill The Past, the Cultist appears as a tumbling skeleton. This is the default timefall animation for characters who do not have proper sprites for the sequence.
If the option "Increase Speed When Out Of Combat" is activated, the speed of both players will be increased during the Cultists past. This is because the criteria for being 'out of combat' depends on the presence of enemies, and does not account for pvp combat.
The guns in the cultists past can run out of ammo, despite the game not showing the ammo counter. If out of ammo, the Magnum can be thrown to deal a half heart of damage. Thrown magnums can be picked back up by either player.
The Cultist's blanks and armor will carry over into their past, giving them an advantage over the protagonist during the final duel.
It is possible for one player to take both guns in the past for themselves, rendering the other player defenseless.
The Cultist cannot begin the speedrun timer. This makes it theoretically possible to beat the game with 0 seconds on the timer if Player 1 can be killed in the first room.
The only NPC that will not meet the Cultist with a rude dismissal is Winchester when encountered in the Gungeon. If spoken to in the Breach, he will be as flippant as the rest of the NPCs.
If the Cultist is alive during the Punch-Out phase of the Resourceful Rat bossfight, he will not be able to help, being tied up and helpless next to the bomb.
Nicknames that NPCs use to refer to The Cultist include:
Somebody
Some guy
Rando
Extra
Guy next to the protagonist
Assistant gun user
Additional set of hands
Trivia
The Cultist's Dart Gun resembles a purple version of the Nerf "Maverick".
The Cultist is likely modelled after the Gun Cultist enemy.
Cut Content
In the asset files of Enter the Gungeon, there exists a boss splash screen portrait and map icon for the Cultist in grey robes, looking far more like a Gun Cultist enemy and carrying a real gun.
Gallery
The Cultist in-game.
The Cultist's alternate costume.
The Cultist during the boss splash screen.
References
↑"After a clumsy child of the Gungeon accidentally dropped this toy into a pit, they were forced to amuse themselves with the Dart Gun." - Ammonomicon description of the Light Gun
↑"Just because children are young, doesn't mean they don't have pasts they would like to change. Perhaps some young soul wished to make sure his or her sibling took the blame for spilling grape juice on the couch. Much less worthy causes have been championed in the Gungeon." - Ammonomicon description of the Dart Gun
