You have befallen under the curse of lycanthropy, as a wererat. Under the new moon you transform into a giant rat. Additionally you gain the following benefits:

Damage Vulnerability: You get the vulnerability to damage dealt by silvered weapons.

Keen Smell: You get advantage on Wisdom (Perception)checks that rely on smell.

Shapechanger: You can use your to polymorph into a rat-humanoid hybrid or into a giant rat, or back into your true form. You can use this feature twice per long rest. While you are transformed the following rules apply:

Beast form:

• Your game statistics are replaced by the statistics of the giant rat, but you retain your alignment, personality, and Intelligence, Wisdom, and Charisma scores. You also retain all of your skill and saving throw proficiencies, in addition to gaining those of the giant rat.
• When you transform, you assume the Giant Rat’s hit points and Hit Dice. When you revert to your normal form, you return to the number of hit points you had before you transformed. However, if you revert as a result of dropping to 0 hit points, any excess damage carries over to your normal form. 
• You can’t cast spells, and your ability to speak or take any action that requires hands is limited to the capabilities of your beast form. Transforming doesn’t break your concentration on a spell you’ve already cast, however, or prevent you from taking actions that are part of a spell.
• You retain the benefit of any features from your class, race, or other source and can use them if the new form is physically capable of doing so. However, you can’t use any of your special senses, unless your new form also has that sense.
• Your equipment drops to the ground in the place where you transformed.
• As a part of your attack action you can attack once with your claws and once with your bite.

Hybrid form:

• Your DEX becomes 15, unless it already is higher.
• Your AC becomes  12 + your DEX modifier, unless you are wearing armor.
• You cannot speak or cast spells that require verbal components.
• As part of your attack you can additionally attack with your claws or your bite.
• You gain 60 ft. of darkvision.