Magical terrain, disease, necrotic, airborne


Infected (Stage 1): Whenever you take necrotic damage from any source, or from any claw or bite damage from a fiend, you must succeed at a Constitution saving throw with a DC equal to 8 + the damage dealt. If you fail, you are infected with a magical disease called soul rot. You take 1 level of exhaustion, your speed is reduced by 5 feet, and your alignment shifts one step closer to evil.
Infected (Stage 2): If you take additional necrotic or fiend claw or bite damage and fail a second save against soul rot, you suffer 1 extra level of exhaustion, your speed is reduced by half, and your alignment shifts one more step toward evil. If you are already evil, your alignment now shifts one step closer toward lawful (if a devil infected you) or chaotic (if a demon infected you).
Infected (Stage 3): If you take additional necrotic or fiend claw or bite damage and fail a third save against soul rot, your alignment completes its journey to evil if you were originally good, or from law or chaos if you were originally evil. The two levels of exhaustion previously imposed are removed, and you feel better than you ever have – like a brand new version of yourself, free from the chains of your past. You have no desire to restore your alignment and attempt to hide the change from your allies, friends, and family, even as you seek out new, like-minded evil companions. This in no way means you are obligated to be friendly toward the fiend that infected you, or to fiends in general, or to any evil creatures. You might instead become increasingly intolerant and willing to take extreme, selfish measures to ensure your needs and goals are met, the whole time thinking you are a hero and doing what’s necessary or right, or even that your actions are for “the greater good.” Why can’t your old friends and allies understand that?

Cure: You need a greater restoration or heal to free yourself from soul rot, but will resist any effort to seek them out or have them cast on you. You prefer lies, excuses, or sneaking away over violence as a means to avoid receiving the cure.
Duration: This contamination continues in you even after you exit this terrain, and even after you destroy or defeat the primary monster, villain, or object (relic, etc.) that created soul rot.