If you are useless playing as the monster... Like me!
Then the easiest way to do this is as follows:
Solo - Custom - Map and Mode - Arena - (Any Map)
Then go to extras:
Select "Favours Monster" for difficulty
Strikes set to 0
Battle Wins Required 1
Monster starting armor 100%
Monster starting stage 3
And start the match. I did it as Goliath, first time. Just be sure to take down the medic first!