Zaalbar under a Zeta Carth lead can be a handful if you don’t bring the proper debuffs and potency.
L3-37 is very tough at high gear levels, with stacking max health when she uses her basic (which she uses a lot due to combination taunt & counter) and a quick self-heal.
Light-Side Scoundrels when paired with Vandor Chewbacca are automatically revived when they die if Vandor is alive, that’s a pain.
Scariff Rebel Pathfinder is quite tanky and has a reliable self-revive, is EXTREMELY under-rated on a Bash Bros squad.
Old Daka at g13 and relics and smart modding with her zeta becomes nearly unstoppable.