Originally, if you had Lumi - you were good to go on the 7* challenge. Then they changed it and 5* and up was hell (bc Lumi's heal status would be stolen). Since, it's been nerfed (supposedly) and 6* and 7* allow you to easily beat Yoda without much of a problem.
I've heard of people who just leveled up Lumi, Eeth, JC, JKG, and QGJ and done it.
My time is Lumi, Ahsoka, Eeth, Old Ben, and either JC/Bariss.
I used Luminara, QGJ, Old Ben, Barriss and Eeth Koth. If I had to do it another time, I would probably use someone else like Anakin and Ahsoka instead of Barris and Eeth.
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I've heard of people who just leveled up Lumi, Eeth, JC, JKG, and QGJ and done it.
My time is Lumi, Ahsoka, Eeth, Old Ben, and either JC/Bariss.
Anakin might be good after they rework him