I would like to draw attention to the example of the cleric who is trying to beat a vulnerable enemy because you interpret him as a cleric's player trying to shoot a shot. However, the rules of the 5th edition offer a direct way to beat vulnerable creatures: the push Action.
The Attack action allows you to perform a special melee attack to knock a creature, either to prone it or push it away from you. If you can make multiple attacks with the Attack action, this attack replaces one of them.
The target of your push may not be more than one size larger than you and it must be within your reach. They perform a strength (athletics) test which is challenged by the strength (athletics) or skill (acrobatics) testing of the target (the goal chooses the fitness for use). They are automatically successful if the destination is deactivated. If you succeed, you too Tap the target in prone position or slide it 5 feet away from you.
–Push a creature, Handbook of the Player, pg. 195
Just to eliminate confusion, this type of attack is far less good than the function that combat champion fighters receive, which is better because
- It deals [a lot of] Damage; on push does no harm at all
- The [Strength] The saving throw the goal has to make is harder to achieve than the skill competition with one pushThis allows the target to use either strength or skill and maximize the likelihood that it will have a value that counteracts the shock.
If a player tells you that he wants to do something unconventional, first read the books, because many "uncommon" actions in combat are perfect rules, regardless of whether the player is familiar with the rules or does not know what those rules are are.
Strahd can not be killed directly by a heart stake. Vampires in the 5th edition borrow many of the tropics of classic vampires, but to kill a vampire in the 5th issue, it's not enough to bet them, unless you've already successfully reduced them to 0 hit points and set them while they are rejuvenating at their resting place. Players may like to try to cause as much damage as possible with the tools they believe will do the job. Against a vampire who has not been reduced to 0 hits, however, it is not enough to sting with or without missions in the heart points yet.
If you really [think that you] To get rules on how to use "Called Shots" in general, I recommend that you read other posts on the topic like this to better understand the dangers of this kind of house rules. But when it comes to important enemies like Strahd or other powerful boss animal creatures / NPCs, you must first make sure you understand the rules by which these characters can be defeated. You avoid these kinds of calvin ball situations when you master the scenario presented to the players better.