It surprises Stiles as well, to be honest, that Peter just went with it instead of inquiring about it as he usually does. But he doesn't have time to examine it and he'll think about it later.

The plan works and the first one- the one that grabbed him and pulled him under- surfaces. Stiles grabs his knife and takes a battle-ready stance behind Peter.

Another one emerges a few feet away, skin looking pale from the poison and much slower than the first, likely because it'd been in the poisoned water longer than the one that attacked him.

"I'll get this one!" He tells Peter, moving out from behind him to make a go for it while the first is busy attacking Peter. The mermaid hisses at him, face full ugly sharp teeth and menacing glare. It can't move well on land despite needing to be on it to save itself.

It takes a swipe at him with it's clawed hands, slithering away but Stiles is quicker and kicks out, hitting it in the face. The mermaid screeches terribly in anger and pain, and Stiles moves in to grab one of it's arms to keep from attacking him and straddles its waist. It's other hand comes up and slashes his shoulder, causing him to yelp in pain but before it can do much else Stiles drives the enchanted iron knife into it's chest once, then a few more times just to be sure.

It's... exhilarating, to be honest. And it both scares and thrills him.