Corruption poisoning in 99 Nights in the Forest is handled by lowering the corruption level fast: destroy corrupted trees, kill corrupted animals, and clear rifts as soon as they appear. The key source material I found says corruption starts in Hard Mode after Day 3, and the most effective counter is actively removing corrupted enemies and objects rather than waiting it out.

What to do

  1. Go to the Research Outpost and use the Research Monitor to track corruption and rifts.
  1. Focus rifts first, since they keep spreading corruption across nearby trees and animals.
  1. Chop corrupted trees and kill corrupted animals whenever you see them.
  1. Keep moving around the map instead of camping in one spot, so corruption doesn’t build up unseen.
  1. If food starts getting spoiled by rot spores, eat fresh food immediately and stock bandages or med kits early.

When it gets bad

Some guides and player reports say that if corruption reaches very high levels, the poison effect becomes constant and your food can become unusable, so the real fix is to keep clearing corruption before it snowballs. One Reddit player also noted that skipping rifts for even a day makes things much harder, which matches the general advice to clear them regularly.

Quick rule

If you remember only one thing, make it this: clear rifts daily and destroy anything corrupted immediately.

TL;DR

  • Unlock the Research Outpost and track corruption.
  • Kill corrupted animals, chop corrupted trees, and clear rifts.
  • Don’t let corruption sit overnight, or poisoning gets much worse.