Last night Something Blue happened in my game... What an emotional rollercoaster (for me at least)
First, they didn't let Ireena get in the pool. I was shocked! I described the pool shimmering even though there was no sun, an apparition of a handsome young man with a noble visage, Ireena calling him Sergei, all that dialogue in the book... I really thought the intent would be obvious, but the players nope, kept her away. Especially when the water hand comes out. I'm not a native english speaker nor a storyteller, but I would think my skills were enough to impart this... But nooo. Now I'm stuck with her... Good thing is that now Strahd won't rest until he take her out of the picture.
Well, for one thing the players didn't have time to chat with the locals (not that they would anyway) because she heard the voice and ran away as they were taking the wine to the burgomaster's cellar. But on the previous session I had made them remember the card readings again, along with Rictavio's interpretations, hoping that they would keep them in mind and actually know about the *SACRED POOL*.
So, a big lightning bolt destroys the pool and the gazebo, uncovering something shiny. The clouds form into a giant face that says "she's mine!" and out of the mouth comes a black horse with flaming mane and a rider. While he's approaching, the monk goes and grabs the holy symbol. I made him and the druid/cleric roll religion to learn that it's a holy symbol but that only clerics can actually use their powers.
The fight was amazing. When the characters manage to land a hit they would see a brief red flash and the wound closing quickly. They did manage to land 40 hit points on the Heart of Sorrow after which Strahd broke the connection (I made them roll insight to notice him doing it, no one did). The druid held up the Holy Symbol of Ravenkind, concentrating hard on it and cast Chain Lightning. At that point, as he channels magic energy I made the symbol activate and emit bright sunlight (the 5 charges power, it was a 3rd lvl spell after all). The spell wasn't cast, but he still spent the slot. From then on Strahd took quite a beating. They all thought that the holy symbol was stopping the regeneration, when it was in fact the broken connection. They will have a big surprise next time.
One big mistake I made was when the drow bard was standing in front of Ireena, Strahd comes to them and casts sleep. To which the bard replies, I'm an elf, I can't be put to sleep

That caused a lot of laughter at the table, great moment. But I forgot that Ireena should have fallen asleep, even before the bard would... Which meant that she was able to run away and hide.
Strahd went down to only 12 hp!!! So he left, steaming from all the sunlight, unable to find her... I didn't want to give the players the satisfaction of "killing" him
I'm really glad I ran this, even on his own (he did call swarms of bats, but they took 4 rounds to arrive).
Now I have a much better idea of how he works, and how the party can fight him. That's the whole point, right?
Also, I'm definitely using @
pukunui's idea of having the Heart of Sorrow grant immunity from sunlight to Strahd. Otherwise he'll be too easy..
EDIT: Party composed of 4 characters all 5th level: Bard, Druid, Monk and Rogue.