Dredge on paper would always beat you. Good thing he’s not a god. You can win by avoiding his shot and not missing... I know crazy but it just might work.
Cripple once he’s low and obliterate while in his ult to take no damage(if timed perfectly)
You counter raum with your high sustain and cripple.
Tips:
Keep medium range
If Raum últs:
use obliterate or ult to counter
If he runs you can cripple him w/5stackDS