The Weak Villain Rule
Villains receive 2 actions and every time a player acts, they have a 1 in 6 chance of receiving an additional action. Roll this check each time a player completes their turn
The Strong Villain Rule
Villains receive their normal action, plus one for every additional party member along with a chance for a bonus.
They take their normal action once per round, and an additional action after each party member acts. They have an additional 1 in 10 chance of getting a double action after each party member acts instead of a single one.