Mantax AND Pridak are the one with the most differences compared to the sets, effectively.
But when we think about this, it is not precised in the story how the pit mutagen affect every life form. There are immune species like nocturn’s, some with resistance like brutaka’s, but it is not precised in the story what is the real resistance for all of the barraki. Maybe can their mutation affect only some parts of their bodies like the face, or their complete body. We will never know, since our canon informations source is “dry”, so we can have all our interpretation. I’m not the only one on this website who did that.
I can explain some of my choices for the curious and the others if they are interested.
I choose to give Pridak a noble apparance in contrast with his set form to accuentate the fact he completely loses his beloved appearnce, and he considers it as an insult made to him.
For Mantax, I raise his shoulder and add him some armor to give a more warrior look.
For Ehlek, considering he’s already an aquatic specie, I followed the bias to consider he’s less affected by mutation, and choose only to add armor and give him a less prohiminent spine.
For Takadox, Kalmah and Carapar, I wasn’t sure what look to give, so I give them a more terrestrial look than they have in their sets form. Maybe I’ll rework them to create more differences.
That’s it.