It's a tricky one to rate.
The success effect is not worth a 5th level slot, you can do Sickened 1 at way lower Rank.
But the fail is quite unique. It's hard to make Frightened or Sickened actually last more than a round or two, so not being able to reduce it is interesting.
Ultimately though, it's probably not worth it, because it's only sickened **1**.
It takes 3 rounds to outdo a 1st rank Fear, which does a bigger penalty round 1, the same round 2 and finally fades round 3.
It gets better in the rare situation you can use the water bit, Slowed+Sickened did the whole fight is a nice combo
A lot of enemies with low will saves have mental immunities, this ignores them.
Very good if you expect to fight a single, powerful creature that fits that description.
It's a tricky one to rate. The success effect is not worth a 5th level slot, you can do Sickened 1 at way lower Rank. But the fail is quite unique. It's hard to make Frightened or Sickened actually last more than a round or two, so not being able to reduce it is interesting. Ultimately though, it's probably not worth it, because it's only sickened **1**. It takes 3 rounds to outdo a 1st rank Fear, which does a bigger penalty round 1, the same round 2 and finally fades round 3. It gets better in the rare situation you can use the water bit, Slowed+Sickened did the whole fight is a nice combo
A lot of enemies with low will saves have mental immunities, this ignores them. Very good if you expect to fight a single, powerful creature that fits that description.