if I remember correctly, the Keoghtom's ointment (I'm sure I'm not spelling it correctly) cures poison too.
Just wait until you start fighting higher level undead like wights. They drain levels and there's no indication that it's happened. Negative plane protection is a must in some of the dungeons and pay attention to when it expires.
I did check some strategy hints, and the recommended solution for level drain is to reload. Seems odd that raise dead scrolls are all over the place, but there's nary a restoration scroll to be found.
Thanks for the tip on Keoghtum's Oinkment (here, piggy piggy.) I've rarely run across it in tabletop, but it's all over the place in Ravenloft. Cures all kinds of things, and packs a pretty good heal too.
To expand on my first point (about rocks/stones) a bit: Slings rock. (Pun intended.) I don't know if it's a feedback problem or something, but arrows and thrown daggers seem to do absolutely no damage unless your front line is in melee. Slings or thrown rocks, on the other hand, can take out enemies from across an outdoor map. It's overpowered as heck, especially compared to the feeble bows. And what makes it even more OP is that if you're sufficiently far away (just barely in visual range), your enemy will not try to retaliate. A single rock doesn't do a whole lot of damage, but they're plentiful and I'm pretty sure do blunt damage against things like skellies and my favorite critter so far, the Bone Golem. Unfortunately slings aren't available at the start of the game, and I have yet to find a magical one.
Bone Golems hurt like hell. Fortunately there are quite a few Fireball wands lying about, and my main character can 'dual wield' the wands. Or if you have one of the mage NPCs , you can equip him/her with a backup wand. And if you have room, it helps to back pedal away from the golems due to the heavy damage and paralysis effect they inflict.
Burning Hands is a pretty cool spell due to its large area effect. A couple will put the hurt on swarms of low level enemies. And it seems like getting caught in your own AoE is not a thing, so you can fling fireballs with abandon.
Some other hints: For dealing with the "Living Walls", stand about 10' away (at an angle if you have to) and throw rocks or fire your sling at them. After the ammo hits the wall, it wall fall to the ground and you can pick it up without retaliation. Rinse and repeat. Lore note: IIRC in the AD&D rules, Living walls could also cast spells or even use ranged weapons, but not here.
Remember your rear line cannot engage in melee, except on the outdoor maps (at least I think that's how it works.) The exception to this is polearms, like the sole mundane halberd I've found so far. Keep an eye out for them, because they're very useful if your back line runs out of ammo or spells. I think only fighters (and their subclasses) can wield polearms, but fortunately Velika has a couple of fighter levels.
I was disappointed to find that while the game does have Tatian/Tatyana as an NPC and companion, she's pretty poor in combat and doesn't have any story role to speak of. That's pretty weird, because she is a very significant character in Barovia and Ravenloft. But she doesn't do much in this game at all.