For the best chance, complete the first mastery level for the Kraken in order to unlock the Wraith.
Go to Solo -> Custom Match, choose Arena with "Extras" settings:
Difficulty Favour Monsters
Wildlife Population High
Strikes 2
Character Perks Off (this might be better on, but I finally got mine whilst off)
Battle Wins Required 1
Battle Duration Infinite
Starting Armour 100%
Starting Stage 3
Sudden Death Off
For skills, put 3 into abduction, 3 into decoy and 3 into supernova (not as important)
Sneak and sniff, getting behind a wall, when you see the medic dash slightly ahead of their team, use abduction on them to increase your distance and active supernova, use single hits of RT (but still fairly quickly) to incapacitate them without touching them when they go down. Now sit on the body and use decoy when available or supernova to scare the reimagining hunters away.
If you're still having trouble, try killing one or two others before trying (though I personally found this strategy less successful)