Theriac

I must recommend Darkest Night. Not only does it more or less floor your opponents' to hit chances but it also debuffs their damage to an extent that even a tanker would envy. It costs a fair bit of endurance for sure but with two DOs, it's not that bad. I only run into endurance problems when I run both DN and Shadow Fall at the same time (defender hero). In my opinion, Darkest Night is the reason to pick Dark Miasma in the first place.

Excellent!

I've noticed that fearsome stare no longer prevents foes from using ranged attacks. I.e. they will cower in fear but still occationally use a ranged attack, even if left alone. IIRC, fear used to work like a semi-hold against all types of attacks, ranged as well as melee. Did this change recently or is it a bug?

Dark blast is rather controllery. You have a cone root in Tenebrous Tentacles, an AoE disorient in Dark Pit (works great with the tentacles) and a cone knockback in Torrent. The tohit debuff in Dark Blast powers can be enhanced.

I recommend some slots in shadow fall, 25% resistance vs psionics, energy and negative is too good to go unenhanced.