Death Ray is a powerful poke and a strong area of denial tool. Use it in combination with Gravity Field to control your enemy's position.
Make sure you choose the right augment at the right time.
Be careful about how close you let Viktor get to you. Viktor's control of the battlefield increases with his proximity to his opponent.
Be aware of how many augments Viktor has upgraded by looking at the color of the light on his staff (purple, yellow, blue, red).