Sourdough the Evil Sandwich was (formerly) Queen Entozoa until they were revealed to be some sort of spirit or energy being who possesses people's bodies for 1,000 years, but because of Wander, they're now a sandwich and now wants revenge on Wander, Sylvia, Lord Hater, and Peepers.
Sourdough looks like an average cheese, lettuce and ham sandwich, with the two olives on it acting like its eyes but its true form is that of an amorphous and glowing purple entity outwardly resembling some sort of slug/dragon hybrid.
Sourdough is a truly evil and purely tyrannical being. It detests weakness and desperation above all else and prefers displays of power and acts of defiance. It admires power and reputation, which is something they look for in its hosts. It's also very temperamental and very protective of its planets.
Sourdough in their true form is capable of possessing another being and taking complete control of their body, however it can only do this once every 1,000 years. Once it possess someone, Sourdough can apparently keep its host alive for 1,000 years until it ready to get a new one. It can even keep something like a sandwich fresh for a 1,000 years and allow it to survive all manner of physical harm only to come back fully healed soon after. However, its current form is completely powerless and defenseless, leaving Sourdough as nothing more than a helpless sandwich that can stay fresh far longer than other sandwiches. Sourdough's true strength though comes from its incredibly old age which grants it lengthy experience, as well as a vast armada and fortune which it has been expanding throughout the centuries. The bulk of its military force is made up of Queen Entozoa's Beefeaters, which have proven to be bigger, stronger and more competent than other minions seen so far.