In the big book of things we can throw at our players, vampires come up fairly often. They are iconic, they are deadly, they have been imagined in many different ways, and they tend to come with specific rules. As a result they make good choices for big bads but also for one-off encounters. Of course, there is quite a lot we can do with these badies and I hope trying to put it to text helps someone out there. Of course I also hope it'll help me think of a new way to throw one of these at my players.
The vampire, as presented in D&D 5th edition and other places, tends to come with a set of rules. They take damage from running water, sunlight, holy water, die from stakes to the heart, and whatever else you want to give them. Don't want to let them enter a residence without invitation? Also good. What's nice about this kind of thing is that can result in different approaches, and player hitting above their level by exploiting the weaknesses of the creature. They don't need to kill the vampire. They just need to survive until morning, for example. Not every vision of vampires has the same weaknesses and rules they need to follow, but thinking about these can lead to very interesting situations. A classic one is where the party is trapped in a building besieged by vampires who are trying to charm someone into inviting them in.
Of course, magic items are a great way to exploit weaknesses. With something similar to a sun blade a level 1 party has a chance against a vampire spawn. Now, the magnitude may vary depending on the rule system, but it will still help (it still won't be a good chance in D&D 5th edition). You can also easily come up with other anti-vampire magic items. All they need to do is give off sunlight. I fondly remember a lantern that gave off sunlight in one of our campaigns.These may be too powerful, so you may want to make holy water easily available so that they can test for vampires. Alternately, a magic lantern can reveal the true appearance of these baddies.
Long Running Campaigns
These kinds of rules and constraints can be very helpful, especially when making a long running campaign. Going from thralls to weaker vampires to vampire leaders presents a natural evolution over the course of a campaign. The same can be said about going from trying to exploit the weaknesses of vampires to outright head on assaults against their headquarters. That they are presentable, social, and manipulative is also something that is easy to exploit for a campaign. Such an adversary lends them to have long running schemes like a lich, but also able to easily be in the forefront of their plots. Their ability to easily make new spawn also makes them a consistent threat, as well as a reason to fear death at the hands of one.
There are quite a few different variations of vampires out there that we could use. A large swarm of vargouilles can be an interesting situations for lower level characters to fight against. I always considered them to be rather vampiric in nature. Of course, mythology is full of many vampiric variants. Perhaps a sorcerer who had a taste for blood became a vampire in your campaign? Would they have an immunity to sunlight if they did? All good questions that can lead to interesting campaigns. Technically this also wouldn't be a monster like the vampire in the manuals. However, it is still vampiric in nature and could help create a new interesting villain. I recall one game where a creature was attacking people and draining their health through their dreams. The solution involved a dream battle where belief rolls were used to allow players to do impossible things, such as spider climb without casting the spell, and killing it in their dreams. The great thing about these creatures is that playing around with the concept can lead to a new adventure idea. It also makes sense that a vampire would look for ways to mitigate their weaknesses.
Since vampires tend to be smart, charming, and long lives, they present interesting relationship structures. You could easily have a city full of vampire spawn that keep wreaking havoc, but no sign of the vampire that leads them. They could work alone and have everyone working for them without their knowledge. They could also have goals unrelated with domination, such as a hedonistic delight in taking blood. There was one campaign I played in where the vampire was living on the street as a pickpocket and a rogue. It would take out easy targets in order to remain less noticeable, but was acting purely for its own enjoyment.Vampires are intelligent as well so complicated vampire societies with civil wars while being under attack by non-vampires could lead to interesting situations as well. However, the relationship between the vampire(s) and their world tends to be important.
As written, vampire spawn can be freed when their master dies in D&D 5th edition. This makes for an interesting low level badie, but it also has a major different from their master variant. These vampires cannot escape as mist back to their coffins. They have one chance at life and as such, you'd expect them to be more cautious and probably use henchmen. Or maybe they are more animalistic. Regardless, you probably wouldn't expect to see this type of vampire act the same way.
Vampire Hunt Adventure Idea
A vampire is terrorizing the village at night, but the people don't know where the vampire hides during the day. At night they may be under siege and find a house to hold down in while blocking all the windows. Investigate, fighting off the vampire's henchmen, and try to stake the vampire (probably best to go with a vampire spawn here). Could end with a combat encounter in a room with windows, allowing the players to hide in the light to keep the vampire away or drag it into sunlight. Also could end with them staking the vampire in their coffin. If these aids are given, being a level or two below the recommendation is probably a good idea or it may be too easy. Alternatively, fighting the vampire in a head on fight before it tries to leave the town and set up somewhere else could also work.
Vampire Ship Adventure Idea
A vampire is moving from city to city in a boat, claiming a few victims, and then moving on to a different port. The players need to investigate the cause, track it down to it's old hideout, which heavily suggests it's a vampire (probably a vampire spawn if you want to run this at a low level), and then try to hunt it down out in the world before it changes locations again. This will probably be more episodic in nature and have a few false leads.