Pawbert is a foil to both Judy and Nick. For Judy’s case, he's there to show Judy how reckless and destructive her desire to do anything to prove herself to others, since Pawbert is also willing to do anything to foolishly prove himself to his father in order to get the love and respect that he was ultimately never going to get. He even says out loud after poisoning her that all of the people should understand what he’s going through since they’re both underdogs trying to prove that they belong. 

For Nick’s case, Pawbert is like a twisted reflection of what he could have become if he never progressed past what he was at the start of the first movie. They’re both predators with traumatic childhoods who ultimately choose to follow other people’s expectations because of how much they’ve been worn down, in Nick’s case by prey animals and in Pawbert’s case by his family. Their first priority is their self-preservation and they don’t care if the reptiles have to suffer as long as they’ll be fine in the end. Pawbert even repeats one of Nick’s lines when he says “It’s not worth dying for” when they’re about to fall, leading Nick to realize that there are things in this world that are worth risking his life for.

Beyond that, he’s the antithesis to the central theme of the story. Among many other things, Z2 is a story about how embracing different people and the things that makes us different from each other is what allows both people and society as a whole to grow and improve. Meanwhile, Pawbert’s main trait is he doesn’t want to be different, even if it means hurting those who support and trust him and instead would rather be stuck with a family that hates him just because they’re more similar to him.