Seeing Seraphine and Merlin work together is one thing, but seeing them ultimately defeat the wasteland monster is another – or so how Seid's thoughts went as he watched the whole thing from the sideline.
For the most part, he was still worried about Seraphine's safety. Though he could easily capture their target without putting any effort, he decided to let her and Merlin finish it themselves, directing his focus on guarding her instead. While ending the chase once and for all would've been an easier way to keep her out of harm, he realized that she's also being tested that whole time.
Merlin may appear too occupied with the pursuit of the wasteland monster, but Seid could see how his attention would divert to Seraphine from time to time.
Observing. Contemplating. Assessing.
