Finally got a mythical starfury emerald tonight, can these two skills be combined for a viable mage hunter?
Absolutely. I haven’t gotten around to making them yet, but I’ve got a few variations of roh/tss mage hunter and the damage looks like it could be real nice
Sustain/defense is an issue though, be prepared to run a lot! Also I wouldn’t suggest doing it unless you have a few decent items for it
While i haven’t made one myself i suspect you’ll run into some RR issues - namely the choice between Starpact (super important for trozans) or Censure (your only mastery based source of RR in the combo). To me it just seems like it’d be a frustrating combo vs any naturally cold resistant enemies or any enemy with a prismatic/sheltering item equipped.
A possible build idea for you:
https://www.grimtools.com/calc/r2B6YKD2
I’ve started leveling this character but have yet to finish. Don’t have much time for the game these days.
Note: Double rare greens are somewhat impossible to find with the prefix/suffix you require. Best to aim for the suffix ‘Fallen Skies’ for the sky fragment proc (in my opinion). Proc’s provide good additional damage.
The toss-up between Star Pact & Censure is up to you. Personally I go for Censure for the -RR (+ Devotion proc’s providing additional -RR) as the 4-piece Trozans & Offhand provide -0.8 seconds cooldown (CD) on Trozans Skyshard (TSS) along with +25% CD reduction from gear. This gives ~1.65s CD on TSS which for me is enough.
Note also this build is not designed around Crucible.
All the best.
nice work with the build! I would certainty having fun playing it 
I would personally get Mirror up to 12/12 though
Compiling that many good greens would take me decades. But I bet launching all those comets would be fun!
I have many “of fallen skies” items, it is the same skill so if you have 3 of them it is basically 15% chance on attack, and the skill has cooldown.
It certainly would!
As I mention, just aim for the suffix ‘Fallen Skies’ on gear, the prefix can be whatever works for your build. Otherwise, if you use mods such as GD Stash, you can craft the perfect double rare green (which sometimes I do just for fun).
As malawiglenn touched upon, #skill points in mirror is a personal preference. As I don’t normally play Crucible, a couple of points is enough for me. The contray, yes I’d max it.
Have fun.