Koga is fast and hard to target, plus he is able to remove marks by dashing. Fight him at midrange to keep him from getting behind you. I recommend getting at least harmonious 3, his ult will end up healing your full health.
As Barik, drop your Turrets and shield, play a cat and mouse game where youre the mouse, let the turrets do damage meanwhile and keep your shield or cover between you and the turtle.
If you use Agony, stun Torvald whenever he's preparing/starting his Ultimate. He is not CC-immune during his ulti, and stunning him will stop his Ult and can save your teammates from being thrown off the map.