The Young Vampire is a Level 5 villain. Villains and monsters only have two stats - Armour Class (AC) and Hit Points (HP). The Young Vampire has AC16 and 8HP. Villains and monsters move and attack according to one of a number of tactics listed on their cards. Each possible maneuver for a monster or villain starts with a statement. If the statement is true follow the tactics listed. Otherwise, go on to the next statement. The final entry in the list will be the default action if nothing else is true.
To show this in more detail here are the tactics for the Young Vampire.
The Young Vampire activates at the start of each Villain Phase.
If the Young Vampire is adjacent to a Hero, it attacks that Hero with Fangs.
If the Young Vampire is within 1 tile of two or more Heroes, it attacks each hero within 1 tile of it with a hypnotic Gaze.
If the Young Vampire is on a Start tile, the active Hero takes 1 damage.
Otherwise, the Young vampire moves 1 tile in the direction of the tile's arrow.
A Fangs attack gives the Young Vampire a +8 bonus to hit on 1d20 and causes 2 damage. In addition, the Young Vampire regains 1HP and moves 1 tile in the direction of the tile's arrow.
A hypnotic Gaze attack gives the Young Vampire a +6 bonus to hit and causes 2 damage. In addition, place the Hero attacked 1 tile deeper into the dungeon.
A man of noble birth, Strahd spent much of his life serving causes of goodness and law, most notably as a warrior and leader of armies. Years of such service took their toll upon him however, and by the time he reached middle age, Strahd came to believe he had squandered his life and his youth. With this dark mood upon him, he came to conquer the region known as Barovia, and assumed lord-ship there, taking as his residence the pre-existing castle known as Ravenloft. From this position of power and security, he called for members of his family "long unseated from their ancestral thrones" to join him, including a younger brother named Sergei.
Some time after this reunion, the Count himself fell in love with a young Barovian woman, Tatyana, though she rejected his affections in favour of the younger Sergei. Filled with despair and jealousy, and brooding a growing hatred for Sergei, Strahd sought magical means to restore his youth. In a moment of desperate frustration, he "made a pact with death - a pact of blood." On the day of Sergei and Tatyana's wedding, Strahd murdered his brother and pursued the grieving Tatyana until she flung herself from the walls of Ravenloft. Strahd himself was shot down by the arrows of the castle guard. Even so, he did not die, but went on to rule the land of Barovia as a vampire. The master of Castle Ravenloft is known as "the Devil" to the villagers of Barovia.
Strahd is one of the two most powerful villains in this game (the other being Gravestorm the Dracolich) and his stats reflect this. He is a Level 6 villain with AC19 and 12HP. In D&D terms he is classed as being an Ancient Vampire, having lived as a vampire for 400-499 years. As well as being a skilled warrior he is also a master necromancer. As you would expect from so powerful a villain, he has more tactics to choose from (five in all) than any other villain. I shan't list them all but he has two possible attacks - Bite and Magical Ball of Fire. Bite grants him a +8 bonus to hit and does 2 damage. In addition, Strahd regains 1HP. Magical Ball of Fire also grants him a +8 bonus to hit and does 2 damage if it hits or 1 damage if it misses.