Colosseum

For me I have two teams, the one I use the most to get high damage for me is Mandalorian Beskar Armor, Cara dune, snow trooper commander, Grogu, Zeb for one where I get more assists and last longer in general is a full imperial team with the Snowtrooper Commander in the leader ability. That’s just for me personally though.

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Currently,  if you're doing the New Republic, I have had success with the new republic characters as a whole, but i also add Kara Dune instead of Grogu for a more offensive approach. Her 2nd attack is good for buying an extra hit or few throughout the battle because it removes some turn meter...

Grogu in her place is better for removing buffs & adding bonuses...

I have also had success in any Colesseum battle with an all scoundrel squad led by Mandalorian beskar.

Not too many options more.

Rebel fighter team is pretty good too.

But the name of the game in Colesseum is to make slow progress every time unless you purchase shards.

Every 5-10% more improvement means you can gain rewards to level up your newly used Colesseum characters....