Rare and underrated characters that you use or fight in the arena?

I really like Holdo.

She gets off her AoE and dazes a good number, often all five since I've boosted her potency pretty well and no one bothers with tenacity, it seems, then taunts and eats fracture or whatever. If I get more use out of her than that, great, if not--she still served a valuable purpose. I made the switch from zeta Finn to Rey as my leader, so she'll often land a handful of Exposes that R2-D2 will break and land more.

She does her thing and then ensures Trooper, BB8, etc can survive to do their things.