The problems with some shadow cores farming solutions:
* You pay allot of shadow cores in the first place at 'Glaring' or 'Hunting'.
* You need to be very active (manafarm to keep up etc..), and its tiresome !
I've found a nice solution:
* stage M4
* you get 400-700 shadow cores (usually 600)
* you 'pay' 84 shadow cores Looming/chasing shadows=7/orblets=7/haste=7 paying for more for other traits will cost more, give a longer game, and give similar shadow cores stats
* game setup is very simple. place a tower at center-bottom, surround it with amps. Use a gem of yellow(lvl8)/white(lvl5)/red(lvl1) Place amps with yellow level 4 or 5. Just upgrade the center gem, until lvl11.
* place all the time in triple-speed. no enraging. if you call early waves you may get less shadow cores.