Decay potion doesn't allow you to eat anything for 1 minute. No twigs, no potions, no fruit, no meat, no nothing. You can still teleport, cast spells and use scrolls. Stuff Throat would be a good alternate name for this spell. The chance of success is equal to MIN((caster's SP + caster's Magic Bonus) * 3 + 10, 60) - target's MR. In other words, the probability of success is between 0% and 60%. If the target has 60% MR, Decay Potion will never work.

The only way out of it is Cancel Magic. We're not sure if this drop is also on the US servers (we kind of assume so) however, since we reported that Shape Change is dropped by doppelganger, no one has reported getting or even seeing it. If anyone gets Shape Change book or Decay Potion book, we would appreciate an email.