Scalable monsters powers

If they make a hard mode, it would be more interesting to increase the aggression and attack variety of foes rather than make them arbitrarily "harder".

Being that the model they are emulating included several absurd exploits for players to overpower the rest of the game, and should be included as an experience here as well, it's really not going to matter if the foe has more health and does more damage if you whip out an Alucard Shield or spam Soul Steal.

Difficulty is primarily throttled by player choice, especially if the rich variety of options exist here like the best Castlevania games. They could make it a little more interesting by mixing a variety of less overpowered actions that feel more engaging instead of pressing "win". But as an actual experience, scaling foes just protractes the same actions over a longer period.

If in fact you want the foes to remain interesting, making them remain the same despite your scaling is a failure. You either want them to get easier that way you can blast through them more quickly, pile them on so your new found power is manifested in the carnage, change up their behavior that way they present a new challenge, or add new foes to bolster or replace existing foes to increase challenge.

The pitfall is that this could become tedious just as well as entertaining, you may need to backtrack or investigate old areas, and instead of using your advancement in power to make it quick, you find resistance at every step, forward or backward. It might not be as bad if it was every 5th area though.

What we should be most worried about is "Mighty No. 9". While we all hope that Iga will add more to the game and be greater than its inspiration, there's the very real possibility of abandoning the inspiration all together. Castlevania has never been popular for foe scaling, in fact the opposite is perhaps true. Players want new areas with challenge, not repeat areas with annoyance.

We have rogue like modes to bring us fresh challenges, and harder enemies are great, just not the same enemies. It's really just kind of cheap, whereas new enemies, even if their modifications of previous ones, create better recognition of power escalation and measured potency of your own actions.

Modifying a foe can be as little as having ghouls pick up weapons, ghouls now become armed ghouls, or slightly different art, as long as it isn't cheap recolors.

But the easy way is just new enemies randomly showing up in old places mixed in with whatever was there, no new art, no enemy scaling, the new location and unique mixture of foes will create enough challenge on its own.