The easiest way to play bk is to sit in the back-line and throw bombs. If you want a challenge try using the poppy bomb to launch you across to the other side of the enemy and wreck! Don't stand in one spot always be moving!
Viktor's ultimate is reliant on him having direct vision of you so moving out of sight behind a corner or using opaque deployables(such as Inara's wall) will prevent him from selecting your location.
Yagorath is perfect for massive shock pulse chains, she is easy to hit during her planted form and the shock pulse will chain into her team and deal good damage.
A good strategy for this encounter is to hit Zhin with your poison bolts first. Most Zhins will panic counter or billow. After that, it's very easy to burst him down with basics when his defenses are used up.