The Character is Subject to involuntary transformation under the light of a full moon. In such conditions or any time the player is at half health or below and takes damage, they must also succeed on a DC 12 Wisdom or Constitution saving throw.

On a failed save the player turns into a giant were-rat,  tearing the clothes they are wearing and dropping all their equipment in the place they transform. Their alignment also changes temporarily to chaotic evil and they must act in accordance with a blood hungry wererat.

The player may re-roll on a failed save once every hour or at the end of each round when in combat. After making the number of saves equal to your character level +2 you are considered in control of your condition and are no longer susceptible to involuntary transformations due to that specific trigger until the next time you face it.

On a willing transformation you can choose to transform into a giant rat, a tiny rat, or a hybrid form. In the hybrid form you keep your player ability stats with a were-rat's keen senses. You have resistance to bludgeoning, piercing, and slashing damage from non magical non silvered items. In the giant and tiny forms you have all the abilities and immunities of a were-rat. In both forms your stats change as appropriate for shape shifting.

In transformed state you have +2  Acrobatics, Stealth, and Perception. You also have advantage on Wisdom (perception) checks that rely on smell, and on Dexterity saving throws.

As a WereRat, you have to do whatever it takes to make sure no one finds out. Pick from Intimidation, Persuasion, Deception and +2.

Some traits come from the curse, some from the life you had before . +1 to three different abilities.

Lycanthropy shortens the life of long-lived creatures and lengthens the life of short-lived creatures. 

The Lycanthropic curse often leads individuals towards chaos and evil. Though this is not always the case.

Your size is the size of whatever race you were before.

Your base walking speed is 30 feet.

Thanks to your were-blood, you have superior vision in dark and dim conditions. You can see in dim light within 60 feet of you as if it were bright light, and in darkness as if it were dim light. You can’t discern color in darkness, only shades of gray.

You can speak, read, and write Common, and one extra language of your choice.