Can't reach luke level 20

I managed to get to level 20 today, but I agree it's tough - the mechanics of each colosseum boss is essential to account for to squeeze out the maximum points.

For clarity, I'm at 5 stars on Luke, and was at level 19 for the past couple days. Got to 20+ from the Zeffo Guardians and Dryax bears. Or whatever they're called.

For both the bears and the Zeffo guardians, you want to split your damage as evenly as possible. If either bear loses more than 12% of their health than the other (i.e. one bear is at 100%, the other is at 88% or lower) then the lower health bear gets a huge damage boost.

For the Zeffo guardians, if any of them lose all 3 stacks of the unique buff, their next attack gets a huge bump up in damage, which can easily scupper your run if that one uses an AoE attack.

Couple other tips: don't use Barriss' heal, it's so low that it wastes a turn. Open with Luke's mass assist, then have Barriss use her basic. Pass Disciple to Luke, use either of Vader's specials - for the bears, I use special 1 on whichever bear I didn't target for the mass assist - then pass the bonus turn from Luke over to Barriss.

Use her special 1 to hopefully lower the enemy's damage output, then from there it's a balancing act to keep both bears relatively close in terms of health. With this strat I managed to hit around 40-45% fairly consistently, but YMMV.

Hope this helps somewhat, not sure how it would play out at lower stars unfortunately.