So Grubbins has received an update in design!
His past form didn't scream "tough henchman" at all so he's been beefed up and has a better story.

Grubbins is unfortunate in that he was cursed at a young age.
Once his kind reaches adulthood they molt into their final stage, however, Grubbins cannot, despite being an adult he cannot achieve his final form and is very annoyed by this.
Seeking a way to cure his curse he found Agadesh and, ignoring the whole supervillain-y thing, began working for him hoping that his experiments and magic would cure him and allow him to molt.

He is the primary muscle behind Agadesh's plans and often comes to the rescue when his boss can't continue his plans or is foiled. His brawn meaning that no matter how gravid Agadesh may be he can usually carry him all the way back home.

Grubbins ended up loving his work and showing off his beef for his boss in battle. He was even more pleased when he became of better service to his lord gleefully being filled to the brim with younglings, after sharing several clutches of grubs together, he may or may not adore his boss beyond usual loyal henchman boundries.