When Curse of Strahd was released for 5e, I didn't buy it because I already owned owned Expedition to Castle Ravenloft, a perfectly serviceable Strahd adventure. The Expedition to Castle Ravenloft adventure, released for D&D 3rd Edition, was itself a re-release of sorts, of the original Ravenloft adventure. It's a non-linear adventure, with the same kind of flexibility and unpredictability of the original. Strahd could have different (secondary) goals and motivations each game, items of power could be hidden in different locations, the NPCs you encountered could be different, and so on. I've found that Expedition to Castle Ravenloft is still a great resource for running a game in Ravenloft.
For a while, I just ran it in Pathfinder 1e, but lately I've been gaming with players who happen to own the 5e Player's Handbook, so I've been adapting the adventure to 5e. Mostly, you can do the conversion as you play. Instead of using stats in the book, you just open up the 5e Monster Manual, find the monster by the same name, and use those stats. Sometimes, you adjust DC numbers based on feel, experience, and whatever logic you use for DCs in any unscripted situation.
For Strahd and other major NPCs, though, a little extra effort is required. A standard vampire stat block doesn't suit a legendary creature like Strahd.
The Strahd of 5e's Curse of Strahd is different than the Strahd of Expedition to Castle Ravenloft. They're minor differences and probably don't really matter much, but I like the 3rd Edition Strahd better, and honestly I find him scarier. So I've converted Strahd from 3e to 5e.
Medium undead, lawful evil
Armor Class 19
Hit Points 144 (17d8 + 68)
Speed 30 ft., climb 20 ft.
Saving Throws Dex +9, Wis +7, Cha +9
Skills Arcana +15, Deception +9, Perception +12, Religion +10, Stealth +14
Damage Resistances acid, cold, electricity, fire, sonic, necrotic; bludgeoning, piercing, slashing from nonmagical attacks
Damage Immunities As long as the Dayheart remains intact, Strahd suffers no ill effects from sunlight.
Condition Immunities Strahd is able to enter any building in Ravenloft as if he had been invited.
Senses darkvision 120 ft., passive Perception 22
Languages Common, Draconic, Elven, Giant, Infernal
Challenge Rating 15 (13,000) Proficiency Bonus +5
Spellcasting. Strahd is an 18th-level Spellcaster. His Spellcasting ability is Intelligence (spell save DC 17, +9 to hit with spell attacks). Strahd has the following Wizard Spells prepared:
Spellbook. Strahd's spellbook contains these additional spells:
Shapechanger. If Strahd isn't in running water, he can use his Action to Polymorph into a Tiny bat, a Medium cloud of mist, a Dire bat (werebat), or back into his true form.
While in bat form, he can't speak, his walking speed is 5 feet, and he has a flying speed of 30 feet. His Statistics, other than his size and speed, are unchanged. Anything he is wearing transforms with him, but nothing he is carrying does. He reverts to his true form if he dies.
For the Dire bat (werebat) form, use the statistics for the Loup GarouVRG, with the addition of a flying speed of 30 feet.
While in mist form, Strahd can't take any Actions, speak, or manipulate Objects. He is weightless, has a flying speed of 20 feet, can hover, and can enter a Hostile creature's space and stop there. In addition, if air can pass through a space, the mist can do so without squeezing, and it can't pass through water. It has advantage on Strength, Dexterity, and Constitution Saving Throws, and it is immune to all nonmagical damage.
Forest Sign. Strahd cannot be detected by divination.
Mountain Sign. Strahd has a +4 bonus to AC. This is already factored into his stats, but if he loses Mountain Sign then he suffers -4 to AC.
Swamp Sign. Strahd has resistance to acid, fire, and sonic damage. This is already factored into his stats.
Legendary Resistance (3/Day). If Strahd fails a saving throw, he can choose to succeed instead.
Misty Escape. When he drops to 0 Hit Points outside his Resting place, Strahd transforms into a cloud of mist (as in the Shapechanger trait) instead of Falling Unconscious, provided that he isn't in running water. If he can't transform, he is destroyed.
While he has 0 Hit Points in mist form, he can't revert to his vampire form, and he must reach his Resting place within 2 hours or be destroyed. Once in his Resting place, he reverts to his vampire form. He is then Paralyzed until he regains at least 1 hit point. After spending 1 hour in his Resting place with 0 Hit Points, he regains 1 hit point.
Regeneration. Strahd regains 20 hit points at the start of his turn if he has at least 1 hit point and isn't in running water. If he takes radiant damage or damage from holy water, this trait doesn't function at the start of his next turn.
Spider Climb. Strahd can climb difficult surfaces, including upside down on ceilings, without having to make an ability check.
Vampire Weakness Strahd has the following flaw:
Harmed by Running Water. Strahd takes 20 acid damage (reduced to 10 as long as he has Swamp Sign) if it ends its turn in running water.
Multiattack (Vampire Form Only). Strahd makes two attacks, only one of which can be a bite attack.
Unarmed Strike (Vampire Form Only). Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 8 (1d8 + 4) bludgeoning damage, plus 14 (4d6) necrotic damage. If the target is a creature, Strahd can grapple it (escape DC: 18) instead of dealing the bludgeoning damage.
Bite (Bat or Vampire Form Only). Melee Weapon Attack: +8 to hit, reach 5 ft., one willing creature, or a creature that is grappled by Strahd, incapacitated, or restrained. Hit: 7 (1d6 + 4) piercing damage plus 10 (3d6) necrotic damage. The target's hit point maximum is reduced by an amount equal to the necrotic damage taken, and Strahd regains hit points equal to that amount. The reduction lasts until the target finishes a long rest. The target dies if its hit point maximum is reduced to 0. A humanoid slain in this way and then buried in the ground rises the following night as a vampire spawn under Strahd's control.
Charm. Strahd targets one humanoid he can see within 30 feet of him. If the target can see Strahd, the target must succeed on a DC 18 Wisdom saving throw against this magic or be charmed. The charmed target regards Strahd as a trusted friend to be heeded and protected. The target isn't under Strahd's control, but it takes Strahd's requests and actions in the most favorable way and lets Strahd bite it.
Children of the Night (1/Day). Strahd magically calls 2d4 swarms of bats or rats, provided that the sun isn't up. While outdoors, Strahd can call 3d6 wolves instead. The called creatures arrive in 1d4 rounds, acting as allies of Strahd and obeying his spoken commands. The beasts remain for 1 hour, until Strahd dies, or until he dismisses them as a bonus action.
Multiattack (Vampire and dire bat forms only).
Unarmed Strike (Vampire and dire bat forms only).
While Strahd is in Castle Ravenloft, he can take lair actions as long as he isn't incapacitated.
On initiative count 20 (losing initiative ties), Strahd can take one of the following lair action options, or forgo using any of them in that round:
Until initiative count 20 of the next round, Strahd can pass through solid walls, doors, ceilings, and floors as if they weren't there.
Strahd targets any number of doors and windows that he can see, causing each one to either open or close as he wishes. Closed doors can be magically locked (needing a successful DC 20 Strength check to force open) until Strahd chooses to end the effect, or until Strahd uses this lair action again.
Strahd summons the angry spirit of one who has died in the castle. The apparition appears next to a hostile creature that Strahd can see, makes an attack against that creature, and then disappears. The apparition has the statistics of a specter.
Strahd targets one Medium or smaller creature that casts a shadow. The target's shadow must be visible to Strahd and within 30 feet of him. If the target fails a DC 18 Charisma saving throw, its shadow detaches from it and becomes a shadow that obeys Strahd's commands, acting on initiative count 20. A greater restoration spell or a remove curse spell cast on the target restores its natural shadow, but only if its undead shadow has been destroyed.