nesdev.org

Castlevania would crash on me if I had the potion invincibility item and going through a door at the same time. This most frequently happened in the door before Frankenstein, probably because that item drops there. If you timed it right the game consistently locks up while you are going through one of the stages of invincibility.

Yes, in my case, it was the same door.

I don't remember if I had the invincibility item, though. How can you get it right before that door?