Moon Plague Player Rules

(this article is for specific game rules related to player characters. For general lore info, see Moon Plague)

Effects of the moon

The phase of the moon cycles in a fixed two-week pattern, advancing to the next phase every sunrise. The moon phase affects most rolls related to the Moon Plague, including the frequency at which transformations are triggered each night, the difficulty of controlling transformations, and the difficulty of resisting infection when exposed. The DM may adjust figures from the values shown here based on circumstantial factors.

Moon Phase	Transformation Risk (%)	Save DC (base)
new moon	0	8
waxing crescent	0	11
waxing quarter	0	12
waxing half	0	13
waxing three-quarter	10	14
waxing gibbous	20	15
full	80	16
waning gibbous	20	15
waning three-quarter	10	14
waning half	0	13
waning quarter	0	12
waning crescent	0	11

Transformation Triggers

Infected characters are at no risk of transforming until the first sunset on the night of a full moon since the time of infection. At this time a transformation is guaranteed, however the character may still roll to maintain control as normal (see below).
Subsequent transformations are triggered by a variety of events, primarily involving either physical or emotional duress. Note that even if a transformation is "triggered", it is still possible to resist the change via a wisdom save (see below). Examples include, but are not limited to:

• At sunset, roll d100. If lower than or equal to the transformation risk corresponding to the current phase of the moon, a transformation is triggered. If the character is already transformed at sunset, this does not invoke a new self-control check.
• Deliberately attempting to transform (this carries automatic success on the first control check unless done under duress)
• Grievous physical injury (current HP drops to 1/4 of your hit point maximum or lower)
• Grievous physical injury of a close friend or loved one, which you can see or hear
• Powerful emotions, especially primal ones such as anger, fear, and lust
• Watching a close friend or loved one undergo a dangerous transformation

Resisting Transformations

If a transformation is triggered, roll a wisdom save. The DC is based on the current phase of the moon as listed above, but may be adjusted by other circumstantial factors. You may voluntarily choose not to resist the change, in which case you transform immediately (if multiple forms, you choose which) but have advantage to maintain control of your behavior (see below)
You may have advantage on the save if the trigger was expected ahead of time (i. e, having a conversation you know ahead of time will be very difficult), if you have intentionally triggered a transformation within the past 24 hours, if a transformation is very likely to pose a danger to close friends and/or loved ones, or if the DM agrees that other circumstantial factors present at the time would help you. Sufficiently potent calming drugs, spells, and/or potions (such as sleep potions) grant an extra d20 even if you would already have advantage from another source. For example, if under the influence of a sleeping potion which you took ahead of an expected trigger, you may roll three d20s and take the highest result.
Conversely, you are at disadvantage to the save if you have not transformed at all within the past 48 hours, are subjected to multiple triggers simultaneously, or if the DM decides that other circumstantial factors present at the time would significantly hinder you. Sufficiently potent performance enhancing or mind altering drugs, spells, and/or potions (such as haste) force you to roll another d20 even if you would already have disadvantage from another source. For example, if you are both drugged and grievously injured at the same time you must roll three d20s and take the lowest result.
On a successful save, the transformation is prevented with no ill effects. On a failed save, transformation is inevitable. However, if you have not prevented a transformation in the last 24 hours then you may delay the change for a brief time, according to the table below. Note that suppressing a transformation in this way requires significant mental effort, and behaves as if concentrating on a spell. If your concentration is broken, you transform immediately.

Degree of Failure (save DC - roll result)	Maximum Time Before Transformation	Other effects
1	1 hour	If available, you choose between your hybrid or feral forms
2	45 minutes	If available, you choose between your hybrid or feral forms
3	30 minutes	If available, you choose between your hybrid or feral forms
4	15 minutes	If available, you choose between your hybrid or feral forms
5	1 minute	If available, you choose between your hybrid or feral forms
6	2 rounds	If available, you choose between your hybrid or feral forms
7	2 rounds	If available, roll wisdom save to choose between forms
8	1 round	If available, roll wisdom save to choose between forms
9	immediate	If available, roll wisdom save to choose between forms
10+	immediate	forced feral form. disadvantage to control your own behavior

The effects of sufficiently powerful drugs, spells, and/or potions applied while concentrating to postpone a transformation can outright prevent the transformation from happening at all. Note, however, that this still counts as preventing a transformation and therefore prevents you from postponing a change the next time you fail a save within 24 hours.

Controlling Behavior When Transformed

Immediately upon transformation, roll a wisdom save. The DC varies by phase of the moon, as listed above. Repeat the check whenever exposed to a new trigger, re-exposed to a previous trigger, for every round of combat in which you attack someone you would normally regard as an ally, or for every hour of continued exposure. Transformations triggered by the time of day count as "continued exposure" until sunrise. If new triggers are encountered, your new result replaces the old. If you are only suffering continued exposure to existing triggers, you may choose to keep the old result if it is better. In this way most characters can eventually regain control of themselves given enough time, provided that external conditions do not worsen. Sufficiently powerful drugs, spells, and/or potions can also grant additional saves. Such saves are made with advantage.

Roll Results	Effects
Success by 10+	No further control checks while transformed. Can end transformation at will.
Success by 5+	No further control checks unless in combat. Advantage to end transformation.
Success	Full control in combat. Subject to animal instincts outside of combat.
Failure	Subject to animal instincts. If predatory, you must attack an enemy every round if possible. Otherwise, you must flee.
Failure by 5+	As above, but you regard every creature as an enemy.
Failure by 10+	Animal form assumes complete control.

Ending Transformations

If the transformation was not invoked willingly, you may only attempt to end the transformation if you are no longer subject to the triggering event(s). Roll a wisdom save (DC varies by moon phase, as above). Depending on the results of prior control checks, you may either have advantage on the save or succeed automatically. On a success, you may end the transformation at will. On a failure, you may not attempt again for thirty minutes.

RP suggestions

Moon Plague is a direct result of multiple souls competing for the same body. Characters who are particularly in tune with themselves (read: ones that can make a good insight check on themselves) can become consciously aware of the other presence, sometimes even finding ways to communicate with it or give it a name. This can be a double-edged sword; the second self shares your mind, and will know if you attempt to ignore them. On the other hand, willingly giving in to its desires from time to time, even when in full control of your own body, can go a long way towards maintaining control when you really need it. Willingly invoking transformations is a particularly effective way to get on their good side, and has concrete mechanical benefits as described above. Note, also, that your second soul will become aware if you attempt to remove it by any means, and may attempt to resist.

Infecting Other Characters

Since the end of The Age of Coalescence, Moon Plague is no longer contagious.  Patients with "traditional" forms of therianthropy, like werewolves, wereboars, etc, may still pass on that particular affliction by the normal rules for those creatures.

Infection Table

Newly Infected characters used to roll on this table to see which form of infection they received. The DM made this roll in secret.  It is kept here for historical purposes only.

Rules for specific creatures

The monster manual provides rules for the following forms. Use those as written, replacing any rules text regarding infections with those on this page.

• bear
• boar
• rat
• tiger
• wolf

Other creature rules are as follows:

Displacer Beast

Gain the following when transformed

• Your strength becomes 18 if it is not already higher
• Receive a +1 bonus to AC
• Your speed becomes 40 feet if it is not already higher
• As a bonus action, you may teleport up to 40 feet to a point you can see.
• When an effect allows you to roll a save to take half damage, you instead take half damage on a failure and no damage on a success
• multiattack: You may make two attacks with your tentacles in a single action. You are proficient with the tentacles and attacks are based on strength. Damage is 1d6+str bludgeoning damage and 1d4 piercing damage.
• bite: You are proficient with your jaws and attacks are based on strength. Damage is 1d8+str piercing. Targets are exposed to moon plague as described above

Behir

• Your strength becomes 23 if it is not already higher
• Receive a +1 bonus to AC
• your speed becomes 40, climb 20 (hybrid) or 50, climb 40 (feral) if not already higher
• gain immunity to lightning damage
• bite: You are proficient with your jaws and attacks are based on strength. Damage is 1d10+str piercing (hybrid) or 3d10+str piercing (feral). Targets are exposed to moon plague as described above
• lightning breath (hybrid only): You may use a lightning breath weapon attack following the rules normally applied for dragonborn characters
• constrict (feral only): You are proficient with your body and attacks are based on strength. damage is 1d10+str bludgeoning plus 1d10+str slashing damage. The target is grappled if you aren't already constricting a creature, and the target is restrained until this grapple ends.
• lightning breath (feral only): Once per short or long rest, exhale a line of lightning that is 20 feet long and 5 feet wide. Each creature in that line must make a DC 16 Dexterity saving throw, taking 8d10 lightning damage on a failed save, or half as much damage on a successful one.
• swallow (feral only): make one bite attack against a Medium or smaller target you are grappling. If the attack hits, the target is also swallowed, and the grapple ends. While swallowed, the target is blinded and restrained, it has total cover against attacks and other effects outside of you, and it takes 5d6 acid damage at the start of each of your turns. You can have only one creature swallowed at a time. If you take 20 damage or more on a single turn from the swallowed creature, you must succeed on a DC 14 Constitution saving throw at the end of that turn or regurgitate the creature, which falls prone in a space within 10 feet of you. If you die, a swallowed creature is no longer restrained by you and can escape from the corpse by using 15 feet of movement, exiting prone.