Hey, great little demo! I had a lot of fun zipping through the levels and seeing what surprises there are. It inspired me to pull out Castlevania 2 to see if I could finally get through it!

I have some feedback:

• Elayne - Based on the art and material of her on your other sites, Elayne is a character you've breathed a lot of life into! She has a distinct and unique history, personality, appearance, and goals, and she's weird, likable, and relatable. The strength of that character led me to try the demo! However, due to the size and colour palette of the sprite in the demo, almost none of her distinct features come through (body shape, clothing, hair, eyes, expressions, bite marks, equipment, colour palette, etc have almost all been lost by being squeezed into a tiny, brownish sprite), and it's even harder to see when she moves as she moves quite quickly. I assume it's due to simulating the limitations of early console hardware, but I don't think it works in this case as the character has essentially been lost. Also, she controls essentially identically to other early "vampire hunter with a whip" games, so there's another opportunity here to differentiate the character... for example, she could be more agile but more fragile, and she could have some different abilities to further differentiate her (stealth? running movement? sliding movement? wall jump? sword attack for additional short range damage? vampire mode?).

• Whip - I like that the whip has a bit of a delay. It makes it feel more realistic and it requires you to be more careful about how you use it, which adds depth to the gameplay.

• Stairs - I think Elayne moves too quickly on the stairs. If she has the same horizontal velocity on the ground as on the stairs, it means she is actually moving more quickly on the stairs as there is also a vertical component of velocity added. Having her total velocity being lower on the stairs than on the ground would make more sense to me as people generally move more slowly while ascending and descending stairs than on flat ground. Also, a cool feature might be the ability to jump onto stairs, both from the ground and from stairs.

• Goals - what are your goals for the game and gameplay? What's your vision?  A simple Metroidvania type game? Some RPG, or platformer, or adventure elements?

• Enemies - enemy designs are great! The unique styles and movements are fun.  In the third level, the combination of enemies works to ramp up the challenge.

Elayne:

I'm squeezing out one extra colour than is typical, but I don't want to push it too far - as adherence to the NES visual style is important to me. Small details, like her bite marks, are impossible to represent on the sprite, however - they're too small in reality, but would appear almost as large as her eyes when drawn on the player sprite. These details can be better showcased via in-game illustrations, but I haven't been focusing on them since they're not related to gameplay. Any major changes in the sprite design will otherwise have to wait for a potential sequel - as was the norm for NES games. Even Mario's character changed drastically from SMB1 and SMB2.

As for her controls, she does have some differences - some of which you even pointed out. She moves faster than the classic vampire hunters, especially up stairs. She also carries 2 sub-weapons instead of 1, highlighting her greater versatility compared to the classic heroes. 

I have, however, considered adding other abilities in the future (all of which you mentioned): wall jumps, shorter sword attacks, and an extra "power" player state, etc. But none of these are absolutely essential, and will likely wait until a sequel to be implemented. Many of these would affect gameplay balance - like wall jumps, which can break the level design if it's not planned around. I'm also interested in adding a system like "rings" in Elden Ring or the "badges" in Mario Wonder, where you can equip different skills to modify the character a bit, while ensuring the player doesn't have access to too many at once. But again - potential sequel.

Stairs:

Elayne's speed is 1.2 when grounded, but 1 when on stairs - so she is technically moving slower. But unlike the classic games, her speed is much smoother when on the stairs, whereas the classic games would have the hero stop moving after every step - which is likely the biggest reason for why she doesn't feel so slowed. This is done for four primary reasons.

1. I think the smoother movement feels great. This is also something that the "Bloodstained: Curse of the Moon" games do.
2. It helps to better communicate the character's general speed and self-control despite the "stiffness" of a CV-like. She's faster than the heavy Classicvania heroes, coming a little closer to the more OP Metroidvania heroes (who move up stairs much faster too).  
3. It makes stairs feel a bit less scary to less-experienced players by giving them extra control (while still being forced to the other limitations of the stairs), and allows me to use stairs much more often in the level design without it slowing the game down too much.
4. The distance traveled on stairs is 1px per frame (both vertically & horizontally). I do not want to introduce sub-pixel movement while on stairs.

I may choose to allow an optional upgrade (in a potential sequel) that allows players to jump on/off stairs, but that is not essential. I don't like how this lets players skip interacting with stairs, but many players ARE fond of this ability. The biggest barrier to implementing this is: stairs aren't physical objects in the world, but a change in player state... So I'll have to do a bunch of math to determine when the player should be able to land on a staircase mid-jump (a lot of work).

Goals:

The current goal is simple: I'm just trying to make something that could have conceivably been made on the NES - a fairly standard platformer. This is my first game, so I'm trying to keep things as simple as possible and avoid scope creep. That means there won't be too many systems or narrative elements in this first game.

I may broaden the scope into a more open world environment in the future, though perhaps much closer to a Zelda 1-2. I do not plan to incorporate elements like unlocking new navigation abilities (like double jumps) or RPG systems that encourage/require grinding stats, as I prefer the moment-to-moment gameplay feel of the Classicvanias over the Igavania titles. Larger design scopes like that can wait until after I've developed a working engine, however - then I can iterate over time.