Resourceful Rat's Lair

The Resourceful Rat's Lair (only referred to in-game as ???) is a secret chamber in The Gungeon, accessed through a hidden passage found in the Black Powder Mine. It requires at least one key, two blanks, and the Gnawed Key to enter. As the name suggests, it is the domicile of the Resourceful Rat and as such, nearly all floor features are themed around him. This includes the map only showing an animation of him holding a piece of cheese on a fishing rod and even the loading screen when entering the chamber.

Throughout the chamber, the player will encounter numerous rats holding candles. While these rats are harmless under normal circumstances, dying instantly upon player contact and occasionally yielding money, they can be jammed if the player has any curse, which will cause them to deal contact damage.

Like Bullet Hell this floor features no shops and no chest rooms (Unless one counts the reward room after beating the boss).

How to access
Reaching the Resourceful Rat's Lair requires the Gnawed Key, a key to open the trapdoor (or any key replacing items like Shelleton Key or AKEY-47), and 2-3 blanks (or an explosive item or weapon that can open secret rooms).
 * In the Black Powder Mine, a room will have 2-4 rats running on the ground, as a hint. In this room there will be a locked trapdoor hidden by dust that can be revealed by walking on the respective tile multiple times, spraying it with Goop, water from the Mega Douser, or using a blank in the room (short-range blank effects, like blank bullets, will not reveal the trapdoor). A larger than normal dust cloud will appear when walking over the respective tile.
 * After unlocking the trapdoor with any normal key or key-replacing items, falling down it leads to a minecart on a track. Ride the minecart (or walk on the track) to the end, then use a blank to reveal a secret passage (activating a blank effect anywhere including the area before the track will reveal the room). Alternatively, if you have armor, taking damage (by falling into the pit) will reveal the first secret passage.
 * At the end of the secret passage, use another blank to reach a room with another locked hatch.
 * Alternatively, Bloodied Scarf can be used to teleport past both passages without using blanks.
 * Armor cannot be used to open the second passage unless the player has other means of damaging themselves as the first passage is considered a separate room from the one with the pit.
 * Open the hatch with the Gnawed Key and enter it.
 * Entering the Lair for the first time will unlock the Weird Egg.

Layout
Upon entering the floor, the player must fall down the hole in the room to the right to enter the maze.

Maze
The maze consists of an endless grid of square rooms filled with enemies. The player must use the clues from the six Infuriating Notes in the Ammonomicon to determine the correct sequence of directions to travel. Each note ends with a piece of cheese pointing in a specific direction, and the six directions are in order of the six notes in the Ammonomicon. If the directions are successfully followed in order, the player will reach the Resourceful Rat. However, if the player wanders too long without finding the Resourceful Rat, they will simply be taken to an elevator to the Hollow. If the player attempts to take a shortcut in their path (e.g., if the path in the Infuriating Notes is up, right, up, left, left, left, and the player attempts the path up, up, left, left), the final room will contain the elevator to the Hollow even though both paths lead to the same room.

Since the correct sequence required to find the Rat is randomly generated, copying the route of another player is ineffective. However, once the correct route to the Rat has been found, it will stay the same for that player on all future playthroughs.

Fight
See Resourceful Rat.

Post-Rat
After the Resourceful Rat has been fought, the player will be taken to a room with eight pedestals with 2 keys, 1 Glass Guon Stone, 1 Blank, 1 full heart, 1 armor, 1 ammo box, and 1 spread ammo box, along with four special chests that can be opened with special Rat Keys dropped by the Resourceful Rat. These chests always contain Elimentaler, Partially-Eaten Cheese, Resourceful Sack, and Rat Boots. The room also has a secret room, where a serpent is behind two locked doors that can be opened with Rat Keys.


 * While there are two locked doors, the player only needs to use one Rat Key to feed the serpent.

After leaving the loot room, the player can either head to the Hollow or spend a Rat Key to skip to the Forge.

Enemies

 * In addition, the skeletal rat-like minions summoned in the Resourceful Rat Boss Fight can appear in large quantities.

Rooms
Most rooms in the lair share the same square-like shape with an exit tunnelling on each side. The contents of these rooms are as follows:


 * 2 random Shotgun Kin variants and 1 Mutant Shotgun Kin (all 3 being jammed) guarding an Ammomancer.
 * 2 Lead Maidens.
 * 2 Chance Kin accompanied by a player-seeking Dead Blow.
 * 1 of each Shotgun Kin variant (excluding Executioners and Shotgrubs), a Shotgat and a Creech. Following this either when all enemies are slain or nearly all, a Jamerlengo appears.
 * A jammed Chancebulon. This wave is followed by another jammed Chancebulon together with 2 regular Chancebulons.
 * An on-spawning army of Rat minions.
 * A horde of Spents together with a Gunreaper. After a fair few are slain, 2 Skullets and a Jammomancer join the fight.
 * An empty room.
 * 2 Shelletons.
 * 2 Phaser Spiders.
 * 2 Chancebulons and a Misfire Beast.
 * 2 Pinhead, 1 Killithid and 1 Cubulon.

Every room has TNT, Tables, Coffins and Phaser Spider webs strewn about randomly.

Trivia

 * Despite there being no useable map on the resourceful rat's lair the boss entrance still has a teleporter.