A game master I play with keeps joking about random encounter creatures parents or children coming back for revenge some day. It hasn't happened yet, but I hope it does at some point. Having revenge stories is one of my favorites, but creating a compelling one is an art form.
Thus today I want to talk a little bit about the types of those nemeses and hopefully start a discussion.
So let us divide them.
Righteous nemesis
Have your players done a terrible deed? Perhaps after committing a crime, they had to kill a guard in order to escape? Well, it is always possible that a family member of said guard saw them do it and now he or she wants to bring the party to justice. Depending on the alignment of the party members the resolution to this kind of nemesis can be different. For the evil alignment, the forgiveness is probably impossible. But ultimately the righteous nemesis is a good guy, their anger is justified, but if the party and they join hands to oppose a greater evil, the resolution to the revenge story might not end in a fight with them.
Chaotic evil nemesis
They care not about the laws or morality. The party has crossed them somehow, perhaps they have halted their dastardly work or perhaps they barely escaped death from the party hands. It doesn't really matter, the party must die. Ultimately they know only strength and will stop only if they know they cannot oppose the party. Thus a conflict is almost inevitable and when it comes they will use any means necessary to defeat the party. This kind of nemesis can make for a great boss fight, precisely because of their willingness to do anything.
Racial nemesis
This can be a town or even the whole species. Maybe the party gravely insulted the elves? Maybe they destroyed the shrine to their goddess? Depending on the offense the grudge may lead to anything from the racial nemeses hating the party, to them attacking on sight. This like righteous nemesis can possible be solved peacefully, but it is much harder. It is not a single person that you have to win over, it is the whole race.
Trickster nemesis
This can be a fun one. The party may have offended a spirit or a minor trickster god. In any case, the trickster nemesis doesn't really want to kill the party. They just want to make jokes at their expense. There is a huge variance on how powerful the trickster nemesis can be, depending on that the party might have to appease it or defeat it. But until they do the trickster nemesis will hinder parties plans all the time, in a humorous manner, of course.
Incompetent nemesis
This one is mostly for laughs. The nemesis in question is so incompetent that all their attempts fail spectacularly. The failed attempts might even help the party. They will always swear to try again and somehow escape unharmed until they fail again.
Friend turned nemesis
The party has been traveling with this NPC for some time. He knows all the party quirks and tactics. But at some point, the party does something that makes the NPC turn against the party. This nemesis will doubtlessly use all the knowledge they gained to make the parties life miserable. And it can be especially painful for the players, knowing that their former friend hates them now. Ultimately reconciliation is possible, but he is unlikely to fall for anything but sincere attempts to remedy the situation.
Those are just a few nemesis types. Which is your favorite? What others did you have in your games? What others do you want to try?