Rework damage immunity

Part two, now that you've learned, is don't use the team that steals TM when you see Nest or you will get into the same trouble.

The problem isn't the stun. 

The problem is that you're constantly reducing his turn meter, and unless he takes 2 turns, the DmgImmunity buff will never drop off. 

There are many teams that have no problem here. You can even use 4xRebels + Nihilus. Nihilus won't get many turns, but he won't get none, and if you auto for a minute his insta-kill will come off cooldown. Damage Immunity is not Insta-Kill immunity, so you instakill Jango's first life and then overwhelm him to kill hiim a 2nd time. 

If you're already slaughtering the other teams first 4 toons, it should be easy for a mid-relic Nihilus to stay alive long enough to get that first kill. 

Otherwise just try an entirely new squad, one that doesn't remove TM from enemies, and you'll be fine. 

Now you've learned. Don't bring teams that remove turnmeter to a Jango fight.

Easier if you rework your lineup choices.