Colored Locks
 Obstacles 
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|---|---|---|---|---|---|---|---|---|---|---|
| Rocks and Blocks | Barrels | Poops | Colored Locks | Soot Tag | Lily Pad | Rock Balls | Pipes | Magnifier | Amniotic Sacs | Golden Reward Plate |
Colored Locks are obstacles found throughout all chapters, but are most often found primarily in Chapter 3, as well as in 
Treasure Rooms and 
Secret Rooms. They function similarly to 
Key Blocks, but can only be unlocked/destroyed by the use of a corresponding Colored Puzzle Key, which is almost always found somewhere else in the room. Like regular Key Blocks, they can not be flown over by Isaac or most other flying enemies.
Colored Locks come primarily in 3 colors: Red, Blue and Green.
They are commonly seen either blocking treasure or presenting room puzzles.
Chain Locks
Chain Locks are variants of Colored Locks that, unlike regular Locks, can not be opened with keys, and instead only break if an attached Colored Lock or Chain Lock of matching color is broken.
Each individual Chain Lock can take longer or slower to open than others, which is determined by the room layout itself. In some instances, Chain Locks will have no regular Lock linked to them, and therefore act solely as impassable obstacles.
Gray Locks
Gray Locks and Gray Chain Locks are unique colorless Colored Locks. They do not have a corresponding Colored Puzzle Key to open them with, and can only be opened by a swipe attack from a 
Dungeon Master. Likewise, they mostly only ever appear in rooms that have Dungeon Masters.
Colored Puzzle Keys
Colored Puzzle Keys are unique "pickups" that typically appear only in rooms with other Colored Locks. They can be picked up by Isaac, where they will turn into a ghostly familiar which will follow Isaac around the room. When Isaac touches a Colored Lock that is the same color as the ghost, the ghost will enter the Lock and disappear, which will cause it to open.
Colored Puzzle Keys come in the same 3 primary colors as the Colored Locks.
Attempting to leave the room with a Puzzle Key Ghost following Isaac will cause the ghost to disappear. Re-entering the room that contained the Puzzle Key Ghost will cause it to reappear in its original position in key form, before it was picked up by Isaac.
- The only exception where Puzzle Key Ghosts will follow Isaac indefinitely through rooms is within
The Gauntlet, as they are required to have enough collected from defeating bosses in order to enter the next area.
Trivia
- Colored Locks, Chain Locks, the Puzzle Keys, and their ghosts each appear to have tally marks on them that indicate their type — Red is numbered 1, Blue is numbered 2, and Green is numbered 3.
- Originally, there was a color blindness mode that could be toggled on in the Dead Sea Scrolls menu that would turn the color of Green Locks and Puzzle Keys to Yellow. However, this was removed, as they were deemed as not actually having enough noticeable effect for people with color blindness, and it was difficult to support.
Gallery
The appearance of all Colored Key Ghost familiars.
Unused yellow Key Ghost and Locks. Originally replaced the green ones if colorblind mode was enabled.
