Glad to help. RNG damage spikes means that you win or fail this challenge primarily not because you play good, but how the AI targets your characters. If yoda attacks the same character 3 x in a row, he will die. And that will and can happen. Then it's reset time. A higher health pool on all of your characters means that you can survive more of those spikes. As once one of your characters die, it's over.
What is the best allies? Low damage toons and barriss. Why? Because low damage makes it easier to survive when you have 3 oponents. barriss is good because with her equal heal she actually damages yoda. I think I had Plo Kloon and Guard when I've killed him. Kill his minions always first, retreat when there is high dmg dealers.
Dunno if it's possible with a barriss 4* lead..I've had her maxed for the event. But maybe worth a try if Lumi doesn't work out.