Chests will be your best source of guns and items in the game. They come in a variety of tiers with each tier being distinguished by their color. Generally speaking higher tier chests will have better items, but its very important to keep in mind that this is not a hard and fast rule, some low tier items are exceptionally good, and some high tier items kind of suck.
Most, but not all, chests need a key to open. They are commonly found in two chest rooms on each floor (except Bullet Hell) but can also rarely drop in any room as part of the item drop system. They also frequently turn up in secret rooms, can drop after killing the Shadow Magician, can be spawned by winning Winchester’s game, appear in mirror rooms, are spawned by the challenge, blank and dice shrines, are spawned when the Directional Pad runs out of ammo and will show up extra chest rooms with a locked door (these chests usually aren’t worth getting because they require an extra key to get to and never go up to Red or Black tier).
Here are the types of chests with notes:
Contains D tier items, typically considered the weakest items available. They are also the most common chests and only ones outside of Rainbow and Albern’s chests that can contain more than one item, sometimes 3 or 4 or even more. Extra items are always pickups like money or health, it will never have more than one Passive Item, Active Item or Gun. When found outside of chest rooms they will always be unlocked, but these unlocked chests are not guaranteed to contain an item or gun and might only have pickups. It’s often said that you should always ignore Brown chests, but I disagree, they can have some very good stuff (ie Regular Shotgun, Winchester Rifle, Sling, Double Vision) and the potential of extra pickups is the icing on the cake. If you open one and one of those items is a key it effectively cost nothing to open. Keep such things in mind, but if you have limited keys and higher tier chests are available do open them instead.
Contains C tier items. The next step up from brown, generally more powerful items, and less common. Unlike brown will be still be locked when found in secret rooms or room drop.
Next level in item quality and rarity from blue with all that entails. Contains B tier items.
Even more powerful contents than green chests. Contains A tier items.
Height of item quality and rarity. Contains S tier items.
Ultra-rare chest that’s practically an instant run winner. Will never require a key to open and when opened will spit out 8 items and guns. They will be B, A and S tier only, at rates of roughly 15% S tier, 54% A tier and 31% B tier. The chests themselves have a 0.0333% chance to spawn, so you can go tens of hours without seeing any. Any chest can be replaced with a Rainbow chest, but chests that drop as part of the floor drop system will have a slightly higher chance.
Glitch Chest. Will rarely (0.1% chance) replace regular chests. Cannot appear after Black Powder Mine or in Secret floors. When opened will instantly teleport the player to the next floor, but the only thing they can do there is fight a glitched version of the Beholster, where you will fight two Beholsters at once! After winning this tough fight the bosses will drop a huge amount of guns (8) and pickups, and the elevator to the next floor becomes available.
A chest unique to the NPC brother Albern, more info in NPCs section.
Regular chests have a small base chance to be mimics. If you try to open a mimic it will activate and attack you, opening with a punishing jammed blast for the first three tiers. After that it will start to attack you normally, mimics are some of the few enemies that will follow you into different rooms and are quite tough. A useful part of mimics is that if you kill them they will still drop contents of the chest quality they resemble, so you don’t have to spend a key on them. The Mimic Tooth Necklace item exploits this, transforming all chests into mimics and saving you keys in exchange for tough enemies. Red and Black mimics will have different behaviour compared to Brown, Blue and Green mimics, blasting out concentric rings of bullets compared to the more common variant’s twin revolvers, as such they are generally much tougher, though also slower. Mimic’s health rises with the quality of their chest, and they can even be jammed. Mimic are more likely to appear as the player’s curse rises, their starting likelihood is 2.25% chance to replace a chest, and this rises by 2.1% with each level of curse. They will often give themselves away with subtle motions if you pay attention, additionally the Hunter’s dog will bark at them. It is usually a good idea to shoot a weak weapon at any chest to get the jump on them if they are a mimic, this will also give you an achievement and unlock the Book of Chest Anatomy. If you have the Ring of Mimic Friendship then they won’t attack and any mimic will just be an unlocked chest. If you don’t have this item and see an unlocked brown chest in a chest room (where they are normally locked) that chest is always a mimic. Rainbow chests cannot be mimics, even with the Mimic Tooth Necklace, same with Albern’s chest.
Below, all the varieties of mimic.
Chests can also have Fuses, the likelihood of which also rises with curse(by 5% per point). If left too long the fuse will blow up the chest and it’s contents. They can be stopped by either opening the chest or putting out the flame of the fuse with liquid (Robot’s Coolant leak is good for this).
When destroyed by weapon fire without being opened chests will often drop the Junk item. This is usually useless, but can be sold for 3 casings. Junk also gives the robot a small damage boost (5% more), will buff Ser Junkan, can be given to the Ser Junkan shrine for a piece of armor, will synergize with the Trashcannon and can be needed by the tailor when building shortcuts. As such collecting junk can be preferable than opening poor chests if the player is the robot or has Ser Junkan, or both! Junk is less likely to drop if the player holds no keys (60% likelihood on chest destruction that case, normally its 72%). If junk does not drop it can be pickups like armor, or even very low tier items and weapons. Sometimes the chest will just blow up, leaving nothing and damaging the player if they are too close, so stay back if you decide to destroy a chest.