Lycanthorpy

(Thanks to the Pointy Hat over on youtube for the rules and idea in use)

Infection of the Curse: 

Once a creature is infected with lycanthropy, one week must pass before they are able to transform into their lycanthrope form. During this time, the curse has not yet anchored itself to the creature’s body, mind, and soul, which makes it possible for it to be removed by the remove curse spell. One week after infection, the curse will have changed the creature intrinsically; after that point, only a wish spell or a magical ritual or item specifically made to remove the curse of lycanthropy can rid the creature of the curse.

Born lycanthropes -- individuals with at least one lycanthrope parent -- have been altered by the curse since their inception. The curse lays dormant until puberty, making them unable to shift into their lycanthrope form, willingly or unwillingly, until it awakens. Once the curse awakens, born lycanthropes are subject to the same rules and limitations as any infected lycanthrope, but a born lycanthrope’s curse cannot be removed at any point in their life with the remove curse spell.

Transformation Rules

Lycanthropy in this system is dependent on your Curse DC. This DC represents your struggle to take control of your mind during your transformation.

Your Curse DC changes depending on how you interact with your lycanthropy. Fighting against it will lower the DC, while giving into it and allowing yourself to transform will increase the DC:

Your Curse DC starts at 10.

• When you willingly transform into your lycanthrope form, your Curse DC increases by 2.
• When you unwillingly transform into your lycanthrope form, your Curse DC increases by 1.
• When you successfully resist an unwilling transformation, your Curse DC decreases by 2.
• When you are unsuccessful at transforming back into your normal form from your lycanthrope form, your Curse DC increases by 1.
• When you are successful at transforming back into your normal form from your lycanthrope form, your Curse DC decreases by 1.
• When you lose control of your lycanthrope form when your HP falls below one third of your maximum HP, your Curse DC increases by 1.
• When you successfully control your lycanthrope form when your HP falls below one third of your maximum HP, your Curse DC decreases by 1.
• For each week without willingly transforming into your lycanthrope form, your Curse DC decreases by 1.
• Your Curse DC cannot go lower than 8 or higher than 20 unless otherwise specified.
• If your Curse DC reaches 20, you are permanently stuck in your lycanthrope form, even if you fall unconscious, and only a greater restoration spell or dying can bring you back to your normal form.

Lycanthrope Form:

As a bonus action, you can willingly shift into your lycanthrope form for up to an hour. Your lycanthrope form is a hybrid of your normal form and the animal form of the lycanthrope that inflicted you with the curse of lycanthropy.

While in your lycanthrope form:

• Your creature type is humanoid (shapechanger)
• Your walking speed increases by 5 feet.
• You can cast any spell and use any equipment in your normal form, speak, and wear armor.
• Your Strength or Dexterity score increases by 2 (you choose between the two when you are infected with lycanthropy).
• You gain an amount of temporary HP equal to twice your proficiency bonus.
• You can use your claws or your bite as unarmed strikes. You can use either your Dexterity or your Strength (you choose between the two when you are infected with lycanthropy) for both the attack and damage rolls of your unarmed strikes, which deal 1d6 of slashing damage (for claws) or piercing damage (for bite).

You remain in complete control of your lycanthrope form as long as your HP does not drop below one third of your maximum HP. Once your HP drops below one third of your maximum HP, you must make a Constitution or Wisdom saving throw (your choice) against your own Curse DC. On a success, you maintain control of your lycanthrope form and your Curse DC decreases by 1. On a failure, you lose control of your lycanthrope form and your Curse DC increases by 1. 

When you lose control of your lycanthrope form, you automatically lose concentration on any spell you were concentrating on, and the GM decides if you use your turn to attack the nearest creature to you, regardless of whether this creature is friendly or hostile to you, or if you use your full movement to run away from the nearest threat.

You can repeat the saving throw against your Curse DC to try to regain control of your lycanthrope form at the end of each of your turns.

You can use a bonus action to transform back into your normal form as long as you remain in control of your lycanthrope form. When you transform back into your normal form, you cannot move or take actions until after your next turn, as your body acclimates to the toll the lycanthrope form takes on it. You instantly transform back into your normal form if you fall unconscious (unless your Curse DC is equal to 20) or die.

When a full moon is at its peak, you must make a Constitution or Wisdom saving throw against your Curse DC if you wish to resist an unwilling transformation. All saving throws against your Curse DC are done at disadvantage during the night of a full moon, as the curse is stronger at this time.

Once you’ve transformed into your lycanthrope form, you cannot do so again until you finish a long rest.

Infecting Lycanthropy

A lycanthrope can infect another creature with lycanthropy. This is the most common method for the curse to spread. If a lycanthrope makes an attack with their bite against a suitable creature for the curse to inhabit, the creature must make a Wisdom or Constitution saving throw (their choice) against the lycanthrope’s Curse DC. On a failure, the creature is infected with the curse of lycanthropy and will become a lycanthrope one week after infection. The creature can willingly fail this saving throw.

Not all creatures can carry the curse of lycanthropy. In order for a creature to be a suitable host for the curse, the creature must be a humanoid and it cannot be a natural shapechanger of any kind, such as a doppelganger.