Here’s a little breakdown!
First, the Render Passes:

Ambient Occlusion

Mist Pass

Raw Render
Rendered in 32 Bits, so using Camera Raw Filter in Photoshop i could tweak the lighting until be happy with the results:

My main workflow for compositing in photoshop is basically doing adjustments using masks to selectively affect the way i want
For the fog for example, i’ve first blended the mist pass in screen mode, then tinted to a bluish tint, and masked them all, this way i could paint only the places i think it should be cool to have fog, like near the ground plane and etc
I also did a second layer of fog, this time to desaturate a bit at the distance
For this i’ve applied this same mist pass as a mask for the hue/saturation adjustment layer, this way, the farther come less saturated and also bluer (or the color you want for a haze effect)
Also painted some fog by hand, and some lens effects/light scatters
I also like to use AO pass to blend in the scene, can give some interesting results, i generally apply it using multiply or overlay, then mask it and paint the areas i liked
For the Mystic portal stuff on the second image, i’ve simply painted straight using the default brush, set the opacity to be controlled by the tablet and a hard edged brush, as this things are way random, you can just try experimenting things until you are happy with that
Some glows really help too 

Aaaand i think thats it!
i really enjoyed doing this project in the company of all of you, really motivates me to finish that and not give up, so thanks very much to everyone who take a look or commented here, and sorry for my weird english, I barely know how to speak my own language, so i can only imagine the mess that i made here hahahah!
See you in the next opportunity, Cheers!
ps: hey Blizzard, i’m free! 