D&D 5E Vampire (Bat Form) in a Bat Swarm

[Stalker0]

I had this idea for an encounter. The party encounters a number of bat swarms (from the vampire's children of teh night ability). However, the surprise....the vampire is in the swarm in bat form!

I was trying to think how best to run this:

• One thought was to have the vampire do a stealth check. A failure would indicate that one bat isn't quite as coordinated with the swarm as the rest. Seems maybe advantage would be in order though, I mean were talking so many bats, are you really going to notice just one? Assuming stealth passes, would doing an attack or other key action break stealth and reveal "the lone bat" like normal stealth, or do you think its reasonable to let the vampire re-stealth as a bonus action (after the main action) in such a case?
• Bat Swarms take half damage from each magical PBS weapons, which is protection the vampire does not normally get. Do you think its reasonable if the vampire is in the swarm (but not yet noticed) for the vampire to receive the same protection? Should the vampire even take damage in that case unless specifically targeted?
• A vampire's charm ability isn't really a spell and doesn't seem to have any components (the classic "look into my eyes" kind of thing). The ability does work in bat form. Would using this ability reveal the single bat out of the swarm?

 

[Lakesidefantasy]

What a cool idea!

I would let the vampire hide among the bats, but once it attacked or attempted to charm I would reveal it. Later it can try and hide among the swarms. I would probably not give damage to the vampire that was meant for the swarm unless it were an area of effect and vice versa once the vampire is revealed.

This is not an official answer, just the way I think I would handle it.

 

[iserith]

Unless the players have reason to believe one of the bats is a vampire, then there's no need for a Dexterity (Stealth) check in my view.

I would not have the vampire in bat form take damage unless they are specifically targeted.

Assuming it works in bat form, I would not have this reveal the vampire in bat form while in the swarm.

 

[dvstig]

Personally i use a performance check for the vampire, and players choice of Nature, Animal handling or Insight to allow them to target the Vampire directly. Also i allow crits on the swarm to target the Vampire instead, representing getting lucky. AoE will target both targets as usual.