What might make a good villain for a fantasy role playing game adventure.

There are lots of options for villains in the rich world of fantasy role playing.   Here are some possibilities:
1) Dragons - Dragons are iconic villains and come in many varieties.  They can be vicious and cruel, manipulative and clever, or haughty and imperious.  They live in all different biomes and there are even variants for different cultures (like western dragons vs. eastern dragons)
2) Wizards - The evil wizard is the classic fantasy villain.  Possessing great and broad reaching powers, driven by the need to obtain more magical power, and often surrounded by a horde of lesser minions, wizards fit all sorts of scenarios.
3) Undead, especially Liches and Vampires - The undead are always great villains.  Liches and Vampires are especially good as they are very intelligent and powerful.  Often, they are wizards so they combine more than one kind of villain.  They also typically have the ability to create more of their kind or lesser undead to serve as minions.
4) Devils or Demons - Monstrous beings from the lower planes possessing great power and able to twist mortals to their will, devils and demons make classic fantasy villains.  While they are typically very dangerous in battle, they also have the power to manipulate and corrupt mortals to do their bidding.

These are just some of the options you could use for fantasy villains, there are many more as the domain of fantasy adventure is nearly unlimited.