Rainbow Mode

Rainbow mode or Rainbow Run is a game mode added in the A Farewell to Arms Update, activated by talking to the NPC Bowler, who must be rescued from a cell in the Gungeon after the High Dragun has been beaten at least once.

Effects

Bowler gives the player a Rainbow Chest at the start of each floor, which can spawn items of any quality. The player will be able to grab one of the items, and only one. This is the only source of items throughout the run, and most other items are removed:

At least one and one item is guaranteed to spawn. The remaining items have an approximate distribution of 12% , 41% , 23% , 12% , and 12% .
Items in shops, on pedestals and from The Lost Adventurer and the Gunsling King are all removed.
Bowler will sit on all non-rainbow chests, preventing the player from collecting items.
- Trying to open a chest will make it break, and Bowler will leave a note saying that he took the item.
  - This includes chests from Winchester's game, the Truth Chest, rat chests and paid Synergrace's synergy chests.
- Keys are still consumed if the player tries to open a locked chest.
- Pickups, Lies, Junk and Gold Junk dropped from destroyed chests remain collectible, but other items retrieved from breaking a chest will be replaced.
- If the chest is a Mimic and the player kills it, Bowler will leave a note instead of an item.
- In co-op, Bowler will sit on revival chests, but they will still revive the dead player if opened.
Shrines like the Companion Shrine or gift reward from the Dice Shrine will not work, but negative effects like a heart container removal from the Companion Shrine will still happen if interacted with.
Spawned chests will be replaced by a note.

Exceptions

Master Rounds still appear normally.
Bowler doesn't take quest-related items, such as the Busted Television or Obsidian Shell Casing.
Junk will not be taken.
- This also includes Lies, Gold Junk, and Junkan.
Items are still dropped by the Resourceful Rat during his punch-out phase.
Munchers and the Witches function as normal.
Rainbow chests found naturally still contain items, all eight of which can be picked up.
Using a Shortcut will still provide a selection of three guns, in addition to the starting level's Rainbow Chest. You can take as many of the three guns as you're usually allowed on that floor.
Spice will still have a chance to replace pickups after being consumed as normal.
Knight's Gun will still dig up items as normal.
Spraying the Demon Face with a water gun will still drop an item.
Item that spawn upon clearing a room like Glass Guon Stones are still obtainable.
While most beneficial Shrines don't work, the Glass Shrine will still give the Glass Guon Stones, and the Y.V. shrine will still give its buff.

Notes

The Rainbow Chest doesn't seem to be affected by Magnificence, which means you can often get and ranked items, including the Clone from the chest.
The Rainbow Chests always spawn 4 guns and 4 passive / active items.
Getting a Glitch Chest will still result in going to the next level, making the player fight two glitched Beholsters. However, since Bowler will take all eight rewards usually given by this fight, this is not recommended.
- It is possible for the starting rainbow chest of a floor to be a Glitch Chest. In this case, the chest will still present as a Rainbow Chest and yet when opened will not allow the player to take an item, transporting the player to the next stage with two glitched Beholsters.
If Spice is used, Spice can appear as room rewards and miniboss rewards. It will also be purchasable in shops.
Occasionally, Bowler will appear standing on a chest praising the sun and when you approach the chest, it bursts into flames.
You can encounter the Rift that allows you to unlock the Paradox in Rainbow Runs.
Using a Companion Shrine during this mode will remove a heart without giving you a companion.
The Sorceress's blessing can be activated during a rainbow run, bypassing the need to collect guns from the rainbow chest.
Bowler will leave a note after every boss battle asking if the player got hit during the battle, whether or not they did.
If a player dies in coop mode, single coloured chests may still be used to revive a player, but if the player dies before opening the rainbow chest, it will turn into a revive chest until they are respawned. After that, the rainbow chest will work as normal.
Rainbow Mode allows for a high likelihood of encountering the Clone, even after dying and respawning due to the Clone. This allows for easier acquisition of duplicate Master Rounds, making unlocking Super Hot Watch easier as well.
The following items cannot drop from a Rainbow Mode chest:
Items can still be exchanged with the Ring of the Resourceful Rat.
If you open the rainbow chest and leave the room without taking any items, the Resourceful Rat will steal the items left behind. The rat will steal one of the items and leave a note as usual, but this will also count as picking up one of the items, causing the other seven to disappear and a note from Bowler to appear.
- Interestingly, the rat always seems to take the top right item first.
Defeating the High Dragun in a Rainbow Run will cause a gold trophy to appear in the Breach to the right of Bowler.
Opening Rat Chests for the first time will not unlock Rat Boots, Resourceful Sack, Partially-Eaten Cheese or Elimentaler.

Trivia

The special Bowler pose may be a reference to Solaire from Dark Souls' "Praise the Sun" pose. This is further reinforced by how the chest bursts into flames.
When talking to him in The Breach, Bowler will mention that he wants to get rid of the Ammoconda in Rainbow Runs.
- This references the fact that the Ammoconda is the most hated boss by the community.
Bowler signs his notes with the following aliases:
- The Rain Train
- Rainbuddy
- Bowbow
A run type created by YouTuber Retromation.

Bugs

There is a visual bug with Mirrors that will cause Bowler to appear sitting in mid air in the location where the chest reflected in the mirror ought to be sitting.
There is also a visual bug that can cause Bowler to appear behind the chest he is supposed to be sitting on.
There is a glitch in co-op mode where the two players can grab two different items at the same time. If the glitch is successful, the players should have the items they took, along with 2 other items in the chest on the floor that they can pick up. The players have to pick up the items at the exact same time for this to work.
- Dropping Rainbow Loot obtained this way has a chance to cause it to disappear.
- Occasionally, if timed right, if one player grabs the item on the right, and the other player grabs the top-right item, the majority of the remaining items will actually remain. (Usually all items remain.)
- If a player collects an active item with an active item currently held, the previous active item may disappear.
Despite the fact that most chests spawned as room rewards are replaced by a Note while a Rainbow Run is active, Synergy Chests are not affected by this and will appear as normal, though they will still not give an item.
If Rainbow Mode is activated, talking to Bowler yields two options. Selecting “Just wanted to chat.” causes the old avatar of your character to appear if you are playing as one of the four main characters. If playing as The Bullet, the avatar is instead a black square. This doesn’t affect The Robot, The Paradox or The Gunslinger.

Gallery

Bowler sitting on top of a chest.
Bowler on top of a burning chest.
Shops in Rainbow Mode can sell Blanks, Hearts, Glass Guon Stones and a Map.
Rainbow Mode and a Winchester chest.
Witches encountered on Rainbow Mode run.
Bowler may sometimes be in this statuesque victory pose. If you approach, it catches fire.
Bowler Appears on invisible mirror chests in Rainbow Mode
A visual bug in which Bowler appears behind the chest he is supposed to be sitting on.