Recurring Villains
Source GM Core pg. 66
Enemies come and go, but a nemesis is forever. Consider including villains who can appear multiple times over the course of several adventures. They don't necessarily need to be masterminds. Imagine an unscrupulous mercenary who works for major villain after major villain, or a series of clones deployed over and over by a corrupt corporation or galactic leader. When you create a recurring villain, it's best not to make them too integral to the story since the PCs might take them down earlier than you expect! Have some contingency plans in place.
The advice about roleplaying NPCs applies especially to these recurring villains. As they reappear throughout the campaign, they should change in some of the same ways PCs do. Think about how previous run-ins with the PCs have shaped the recurring villain's emotions and plans. Which PC do they have the biggest grudge against, and why? Do they bear scars from previous battles? Have they developed a countermeasure against a PC's spells or tactics? What's memorable about them?
The advice about roleplaying NPCs applies especially to these recurring villains. As they reappear throughout the campaign, they should change in some of the same ways PCs do. Think about how previous run-ins with the PCs have shaped the recurring villain's emotions and plans. Which PC do they have the biggest grudge against, and why? Do they bear scars from previous battles? Have they developed a countermeasure against a PC's spells or tactics? What's memorable about them?
Villain Goals
Source GM Core pg. 66
Just as PCs have goals, so do your villains. A recurring villain might have a vision for what the world should be and a step-by-step plan to get there. A plan gives you a clear way to progress the plot, and an underlying goal guides you in deciding what the NPC does if their plan goes awry. It can be especially helpful to contrast the villain's goals with those of the PCs. If a PC wants to start a long-haul freighting business, maybe a villain plans to get rich robbing merchant and cargo starships. Just like with the PCs' goals, show how the villain's goal has impacted the world, even in small ways. Try to find ways the villain can make a difference, even if the PCs are successful against them. A villain will look ineffective if the PCs foil every single plot or plan. For instance, the villain might turn a memorable NPC to their cause, set an institution ablaze, or invade a planet.