Come to think of it what are the requirements to be an independant actor anyway?
It varies, normally hero factions and heroes themselves are a example, like Sonic and Tails. Independent or secondary antagonist is a good bet but mostly the rule is that they do not hold territory but this is not a iron clad rule since there are Kings and Princes that also don't rule territory.
However some of them could be extremely dangerous, crises sometimes can be triggered by this independent actors or are the independent actors themselves.
The Moon from Stellar Glow is not a King but a Independent actor as a example.
Independent Actors however have less resources than Princes overall but could seek alliances with other Independents or even Kings and Princes to bolster their power and could even lease themselves to other players in exchange for something.
Ultimately they have less power but have a lot more freedom to explore the world since they aren't tied to a obligations that comes with own a large organization or territory, and most Kings and Princes barely pay attention to them except when they want something.
One may say the Independents are the true protagonists of the setting since sometimes they may seek to depose a King and would have to got to several adventures to find the tools and allies necessary to depose them. That is the goal of normal play of a Villainc Victorious setting that the players, as a new hero of this world, primary objective is to depose the Kings, the main antagonists, by whatever means and tools as necessary even if means allying with other King to accomplish this goal.
See, I imagine they'll become rivals for Eggman's attention. Not his affection, because that is reserved for his children.
Starline already has one in place of Stone and Thunderbolt frankly needs a better friend than Grimer. Starline is many things but even I think he would be sick over half the stuff Grimer did.