[RPG] Will the necrotic-damage-heavy PC be too weak in Curse of Strahd

This Dhampir race is effectively a weaker version of a Drow, so I'll compare it to that.

• Ability Score Increase: The Dhampir gets to choose between the ability score bonuses of the Drow and those of the Dragonborn. This is perfectly in line with existing races.

Stuff the Dhampir gets:

• Age & Alignment: Don't really matter from a balance perspective.

• Size: The same as everyone else.

• Speed: The same as almost everyone else, including the Drow.

• Superior Darkvision: The same as the Drow.

• Sunlight Sensitivity: The same as the Drow.

• Dhampir Magic: The Dhampir gets a 1st level spell 1/day at 1st level, and a 2nd level spell 1/day at 3rd level. The Drow gets a cantrip, a 1st level spell 1/day at 3rd level, and a 2nd level spell 1/day at 5th level. This is the first real difference between the two. The Dhampir gets their racial spells 2 levels earlier, which is obviously stronger up until 5th level when it stops mattering. Not getting a free cantrip goes a fair way towards balancing this out, though.

• Vampiric Heritage: I'll come back to this.

• Vampire Weaknesses: If you're incapacitated in a place of rest, you're probably asleep. It's pretty easy to kill someone who's asleep in general, so this doesn't really change much. There might be niche cases where it really comes into play but most of the time it shouldn't matter much.

Languages: Common and one other, just like every other race. The freedom to choose is nice, but hardly imbalancing.

Stuff the Dhampir doesn't get that the Drow does:

• Keen Senses: Free proficiency in the most important skill in the game. This is pretty strong.

• Fey Ancestry: Advantage on saving throws against some of the most dangerous spells in the game, and immunity to the Sleep spell. This is also pretty strong.

• Trance: Depending on your group and your DM, this might be important, but for most players, it's not going to matter a whole lot.

• Drow Weapon Training: This is kind of nice, but most builds that need weapon proficiencies involve a class that gives them, so it's not that nice.

Overall, the Dhampir is probably a weaker version of the Drow. Their racial magic trait is a little better before level 5, but after that it's the same, minus a cantrip. Now for the elephant in the room.

Vampiric Heritage

Whenever you grapple, incapacitate, or restrain a creature, you gain the ability to bite that creature dealing 1d6 piercing damage. Furthermore, you can spend your turn drinking the blood of that creature, causing it to loss [sic] 1d6 necrotic damage. The creature's hit point maximum is reduced by an amount equal to the necrotic damage taken, and you regains [sic] hit points equal to that amount. The reduction lasts until the creature finishes a long rest, it dies if this effect reduces its hit point maximum to 0.

The problem with this is "the ability to bite that creature dealing 1d6 piercing damage". Does this require an action? A bonus action? No action at all? Does it give you the ability to do that when you grapple them, or anytime while you're grappling them? It doesn't really give us anyway to know.

The good news is that it doesn't really matter. Unless it requires no action and is anytime while you're grappling them, this is a pretty weak ability. If it's free when you grapple them, you can grapple, bite, let go, grapple, bite, let go and so on up to 4 times (if you're a Fighter). Except that you're just dealing 1d6 damage, so you'd have been better off attacking normally. Assuming your Strength score is 16 or higher, you'd have been better off punching them!

It only gets worse with other interpretations, too. If it requires an action and you can do it anytime while grappling, you're effectively using a turn to deal 1d6 damage, which is pretty much a joke.

Moving along to the other half of the ability, we have the ability to spend your turn drinking the blood of a creature. It's pretty clear what "spend your turn" means, and it makes for a pretty useless ability. Using your entire turn to deal 1d6 damage and gain 1d6 hit points might be ok at level 1 but it's going to become a joke pretty quickly.

The reducing maximum hit points part is useless because if you do enough damage to kill them with it, they would have died anyway. In general, D&D characters want to kill things, not inconvenience them. It could be used as a way to prevent an enemy regaining hit points, but there's a cantrip that does the job better and more efficiently.

So, overall, the Dhampir is pretty much a weakened version of the Drow race with some unique but useless features.

TL;DR - Sure, each of your abilities is shared with at least one party member. But that's ok! Overlap is never such a bad thing if used properly. In fact, in many cases, this overlap can lead to a "the whole is greater than the sum of its parts" type of thing.

Here are a few things I can think of that could potentially boost your perception of usefulness in your party :

• You can steal cantrips from other classes. Your tome grants you cantrips from whatever spell list you want and converts them to warlock cantrips (meaning you cast with charisma). This allows you to get Guidance, which is awesome in social encounters (you give a few magical tips to the bard, who can roll an additional d4 with his persuasion roll if it's done in the next minute), as it stacks with the advantage mechanics. This also works with lock picking or other adventuring skills. Guidance is never wasted if you use it properly! You can also get a druid's shillelagh for melee options. In essence, this turns you into a hexblade, allowing you to use your charisma modifier on attack and damage rolls for 1 minute. By this point, however, you likely have already selected your extra cantrips. Perhaps your Patron (and by that I mean your GM) would let you swap them out if you talk to them about your perceived uselessness?
• Increased travel speed. As both you and the wizard can cast rituals (assuming you eventually take book of ancient secrets), Phantom Steed becomes super interesting. Normally, a party travels 3 to 4 miles per hour depending on chosen pace. Phantom Steed allows you to travel 10 to 13 miles per hour, but casting it as a ritual for your whole party would normally mean that your party members would have to travel solo or waste the spell waiting for everyone else. With 2 ritual casters, you can take 30 minutes to cast it for everyone, then travel 5 to 6.5 miles during the remaining half hour. Furthermore, you no longer have to think about horses when going into dungeons, never have to pay for their stabling/food, etc.
• Ritual overlap is definitely not a bad thing. For instance, it would take an hour for a single caster to identify a few potions, a sword and one or two magical trinkets (10 minutes ritual per item), during which time the caster is not taking a short rest. With two casters, you can reduce the downtime considerably, which is important in dangerous territory. Also of note, you are not limited to warlock or wizard rituals. This means that any other caster in your party that learns a ritual, they can (if they want) teach it to you. It's not always super useful to have ritual overlap, but when it comes handy, it can literally save lives. This also means that you can learn ritual spells that are not on the Warlock spell list, such as detect magic. Sure, there's an invocation for that, but you have very few of those, while you can have infinite rituals.
• You should try to synergize with your bard friend. An iconic warlock combo is using darkness and devil's sight to get advantage on all their attack rolls (you see them but they don't see you). However, darkness requires concentration to maintain, so you can't use Hex at the same time. If you can convince your bard to cast darkness for you (or on you, perhaps), you get to increase your damage output significantly.
• Don't compare yourself to the wizard and/or bards in combat. With their vastly larger spell slot allotment, they can decide to burn much more ressources in a single fight than you can. While you do have access to fireball (Fiend patron), they will probably out-damage you if they decide to sling four of them compared to your one or two. On the other hand, if you compare yourself to an auto-attacker (such as a fighter or ranger using a bow, perhaps), the comparison stands much better. With an Agonizing Eldritch Blast, you deal pretty much the same damage as an archer would. While you do not have access to sharpshooter, proper use of Hex should get you very close, especially considering that Hex is "free" to use (no need to sacrifice accuracy, it's just free damage on a hit).
• Your blasts also have utility. At absolutely no cost to you, you can use repelling blast to push enemies away from your party members. This can potentially save their lives! You can also use repelling blast to corral enemies into a clump, allowing your caster friends to use large AoE spells with more efficiency. Some very strong AoE spells are also hard to use because they require enemies to start their round in the AoE to deal damage, or require them to go through a specific area that is obviously dangerous (like a wall of fire, for instance). If you talk to your caster buddies, you can combo off of each other so that these spells can deal damage more than once in a fight as you push the enemies back inside the spells' range.