D&D 5E - Player is playing a Vampire

Burn it with fire? Sunlight? A stake through the heart? Kill them and have them resurrected as a normal human?

In all seriousness, if you're the DM you are expected to and should set limits on your characters. Personally I would never, ever, allow a vampire in my game.

A vampire has a lot of powers and weaknesses that are going to be difficult to plan around. They can't effectively wander around in daylight but they can create minions and turn into fog, etc. Assuming they have class levels in addition, their effective level is much higher than their class level.

There are game systems out there that are designed to handle this kind of thing, D&D is not one of them. If they insist on playing a vampire, I'd create a new "race" following the rules in the DMG with a basis of a weak vampire. At higher levels they can get standard vampire features in place of feats or class abilities. So for example, they don't have regeneration but can do an attack to bite a humanoid creature to get temp hit points.

Someone out there may have something along these lines, but odds are you're going to be winging it.

But like I said, I would just say "no", unless you're willing and able to home brew your own system.

Good luck!

ncG1vNJzZmivp6x7prrWqKmlnF6kv6h706GpnpmUqHyxuMCynKtlmah6sbjAsqCnn12WeretzKmgq51eaYVzf5dvZg%3D%3D