Silverberry one of the cons of the build, was that until you are well geared some engagements (especially Lagon) don’t feel very good. This fight is one of those fights that a lot of people hate doing. My best suggestion would be to have a buddy help clear if your online mode. Try again but really push hard on a single tentacle until he makes you move (with eye beam or Aoe Moon fall) when you see it coming, flame dash to the opposite side and start to wail on the other tentacle. You should be generating enough ward to deal with the tentacle between invocations and your rune bolt strikes. If that fails, pull the single point from “focused rune word” in the rune bolt node. The cast with be “fire lightning cold” for a massive delayed explosion with 800% damage scaling. It’s called Antipode of Mesembria. Invoke that to help hit with bigger invocations. Good luck!