Agony is great against Terminus. He deals a lot of damage to your tanks, and it can be hard for some tanks to escape him. Stunning him gives your frontlines a chance to get away, and makes him vulnerable. Stunning him can also cancel his Siphon.
Sha Lin's ultimate can make him hard to track, but throwing down a Sensor Drone near where he was last seen will reveal him for your team and partially negate his ult.
Strix's stealth can make him harder to track, so toss your Sensor Drones out where you expect him to be and reveal him to your team. If you run the Booby Trap talent, the explosion of your drones can disrupt his aim or throw him off of high ground.