Also nixkins are easy to beat but hard to kill, couple this with assassins/summons/black mirror shenannigans and fireballs lose a lot of their appeal. Well, I agree on fireball being an easy solution to your lack of siege equipment and massed enemy chaff, however you have a lot of options when it comes to city taking, blur+shadow walk and mistofrms being my preferred ones. I'm under the impression that the 'Acheron's chosen' event triggers much more often for the Svart, I've never actually checked but I think it's triggered by the most powerful assassin (marksman) unit present in the whole game world and your sinister trait influences it. Do promote an assassin as soon as you can. Go for esus early and try to remain the council leader as long as you can but never adopt it as a religion, FoL is just too good for you and your recon line is already OP, you have your world spell to give HN (even if Mask is a great little ability).

Also, your racial spell is awesome, you can use it early to stop an annoying neighbour from growing OR cast it later on and give hidden nationality to dozens of nixkins, infinite gold from raiding and no need to declare war! You should always be raiding, never build high tier units, promote them from low tier ones and use your FoL boosted production to go for selected wonders, great economy to support a bazillion units and a couple of science monster cities. Even if unable to take cities they pretty muck wreak havok in the enemy infrastructure and make you filthy rich in the process.

Mages are fine and dandy and Illusionist is a bonus more than an hindrance once you start to play around it but don't underestimate nixkins, they can be an ultra effective defensive/offensive force. Svartalfar are without any doubt my favourite civ, you pretty much nailed it above but I'll add my two cents.

Rise from erebus clan of embers