What build uses this watcher's eye?

why is this 50ex+?

just a good combo or is there a specific build that uses this eye?

I don´t know about prices but it´s very good combo for everyone who plays crit build with hatred.

lot of builds

crit attack builds with phys damage converted to cold damage would benefit the most, but basically any attack build based on phys (except pure phys builds)

spell casters with phys to cold conversion would only lose accuracy from the top potential

theoretically, even cold casters could use it. hatred would be near the same as zealotry for them.. and precision costs only tiny little mana (difference between lvl 1 and 20 precision is only negligible crit chance for them) and the crit multiplier from the jewel is a big deal.

Its good for anyone physical build that doesnt use resolute technique, and all cold casters or even other elemental crit casters.

Ice spears, ice spear totems, glacial cascade, frost nova builds, ice shot bow builds, cyclone, crit lacerate builds (Mathils latest), and many more.

The ONLY downside to it is that it removes brutality as a support for a pure physical build and it doesn't stack with pride, but you cant have everything.