Squeezing into a Smaller Space
- A creature can squeeze through a space that is large enough for a creature one size smaller than it. Thus, a Large creature can squeeze through a passage that's only 5 feet wide. While squeezing through a space, a creature must spend 1 extra foot for every foot it moves there, and it has disadvantage on attack rolls and Dexterity saving throws. Attack rolls against the creature have advantage while it's in the smaller space. 
Sewer plague is a generic term for a broad category of illnesses that incubate in sewers, refuse heaps, and stagnant swamps.
When a humanoid creature is bitten by a creature that carries the disease, or when it comes into contact with filth or offal contaminated by the disease, the creature must succeed on a DC 11 Constitution saving throw or become infected.
It takes 1d4 days for sewer plague’s symptoms to manifest in an infected creature. Symptoms include fatigue and cramps. The infected creature suffers one level of exhaustion, and it regains only half the normal number of hit points from spending Hit Dice and no hit points from finishing a long rest.
At the end of each long rest, an infected creature must make a DC 11 Constitution saving throw. On a failed save, the character gains one level of exhaustion. On a successful save, the character’s exhaustion level decreases by one level. If a successful saving throw reduces the infected creature’s level of exhaustion below 1, the creature recovers from the disease.