Rotta solo is immune to every Coliseum boss' major debuffs***

As the moment I'm writing this the Marquee for Grogu & Anzellans is just hours away and very soon people are unlocking Rotta the Hutt which will be usable in Coliseum

in Rotta's Leader ability:
If Rotta the Hutt was the only ally at the start of battle: He gains 250% Max Health and Max Protection, 50% Health Steal, 25 Speed, he can't be instantly defeated, and whenever he is Ability Blocked, Blinded, Dazed, Feared, or Stunned he dispels it and inflicts 1 stack of Bleed (max 6) until the end of the encounter and 1 Thermal Detonator on all enemies for 2 turns, which can't be evaded or resisted. If it can't be dispelled, he also gains Damage Immunity for 1 turn, which can't be dispelled

***(granted this part is the Zeta meaning only EL 125 and above)

so this means that Rotta dispels the Daze (from Krayt Dragon and Dryax) and the Stun (from Zeffo Tomb Guardians)

for the Jotaz, Rotta doesn't really have any buffs for the Jotaz to dispel

now as Rotta isn't released yet take my words with a grain of salt but basically I think Krayt Dragon is the best matchup for Rotta solo (and conveniently that's what the boss is when he is released) but do ***note that for most players EL 125 is not accessible right away (for all the Zetas)