My Grandmaster Build for Scarlet Keep + Guide in description

The big reason I like Shadebinder is that it can lock down barrier champions preventing them from healing and stunlocking them. Sniper Damage resist is highly recommended since snipers often one shot in GM difficulty. Energy weapons with the Adaptive Munitions is highly recommended for their versatility. Gjallarhorn is fantastic for bursting down wizards, shriekers, ogres, stunned Unstoppables, knights or anything else people usually die to. I usually use the Shadebinder super to clutch revive my teammates while freezing enemies.
Protective Light can be swapped out for High-Energy Fire once you feel comfortable with the GM and Osmiomancy Gloves can be swapped for Ophidian Aspect for more DPS
It's worth mentioning that in Season 17 Resilience got a huge buff. Sniper damage resist may not be needed in Season 17.