I thought Sylens became bad in the end. He had a pretty sinister tone on him.

Sylens isn't stupid. Atm, Sylens has the upper hand. HADES is basically in a spirit form, trapped inside a lantern. At this point in time, Sylens will be wanting to gain further knowledge from HADES. Who knows what deal was made between the two, before Aloy defeated HADES. It was no accident that Sylens happened to carry this lantern, that enabled him to capture HADES' spirit.

Yes @Darth Mauling, but I think Sylens underestimate HADES

I'd say Sylens is very smart but also kinda dumb. He made sure Aloy defeated him when he realized Hades was going out of control which was smart of him. Then he figured out a way to contain Hades and then went back to getting info from him.

The fact that he figured out the lantern would contain Hades was smart but then planning on gaining knowledge and working with him again was a dumb move.

So basically he knows what he's doing most of the time but what he's trying to do isn't always a good idea.

Thats how I see it anyway.

The way is see it is that Sylens is highly intelligent yes, but also has a deep hunger for knowledge hence the “stupidity” that you all are describing. But as Sylens put it “I was ignorant enough to help it but I was never so foolish to trust it.” When referring to hades. After Aloy used the master override on hades it maybe that his programming as the extinction protocol has been removed and now he can only serve as an AI. In other words simply as a data cache and a way to organize and corrupt machines but never without permission from Sylens who probably keeps HADES on a very short leash.

I don't think Sylens is stupid so much as he is willing to take huge risks for even the slightest bit of advancement in his knowledge.