Just a couple of suggestions.

1) Make it Instant Cast. Especially as it is rather slow moving at least make the casting quicker.

2) Let it interrupt and knockback like Thunderblast on each tick.
This would make the Nyx Orb a great bulldozer so to speak, clearing a path to the target.

I know some would say up the damage, but it's a moving AoE and if we can add in the interrupt/knockback it may be a lot more fun/practical to use in some situations without having to argue about tweaking it's damage.