Curse of the Sewers

this can be a curse or a gift, depending on your personal views of such afflictions. Through training your able to control your second skin but still have trouble mastering it give that you will get a random catalyst trigger for an involuntary transformation. The lycanthropy you are afflicted with is Wererat lycanthropy.

Transformation. You can cast the alter self spell to appear in your second form. When you do so, you gain the effects of that spell’s Change Appearance option and cannot end it to gain the benefits of a different option. Casting alter self in this way requires no spell slot, and you must finish a long rest before you can cast it this way again. Your spellcasting ability for this spell is Intelligence, Wisdom, or Charisma. If you have spell slots of 2nd level or higher, you can cast this spell with them. When you cast alter self using this feature, some cosmetic aspect of your second form remains after the spell ends. This visibly marks you unless you actively hide or disguise it. The mark is a perceptible change such as scaly skin, stunted wings, eyes without pupils, or horns. The mark fades after you finish a long rest Involuntary Change.

Certain circumstances can activate your transformation. After you experience this catalyst, at the start of your next turn you must succeed on a DC 15 Charisma saving throw or use your action to cast alter self as described in the Transformation trait, even if you have already used it.