Shadow pure caster. Any help?

Ok i'm trying to use a pure caster instead summoner and i'm very happy now.

As primary damage i'm using Lightning tendrils but i don't know if is very good spell for high levels.
In my opinions there are also arthic breath or glacial cascade.

So i'm explaining my ipothetic 77 points build and ask you some hints to help me.

https://poebuilder.com/character/AAAAAgYAUEI8vSxGRXxtGSL0bAsNjRzcLUdqQ8BUCPS86h1PNbkRUKcrvYJXK_6zjDZh4lVLy70HYx_HLYsreCycVa5Eq4-mghDfsPnogsco-uvuuJPN-nyDES0abJ2upwjjahZvJKo26YCkVdZk5xcv-tIaj_ba-wkZipu1UzUPqxa_5oEmlcSilwYtgz1fUlOX9JeVU1JFnZrgH0EDHg==

Anchio sto provando a chiedere una build da summoner, ma non mi caca nessuno -.-