Regarding the "graveyard duck":
1. The word is in fact "ahiru" (アヒル / 家鴨). It means duck (the animal/waterfoul) -- period. If doing a romhack of this in English, and the translation wants to try and remain as close to the original -- OR be as contextually relevant as possible -- then the word used should be "duck". If you want to change the text to make it more "user-friendly", then I'd suggest referring to the character as a spirit or ghost of sorts.
2. It's in katakana not because it's a name, but because the entire font in the game is katakana. The actual text in the game, when turned from katakana into its proper Japanese equivalent, reads: ストリゴイ墓地で家鴨から絹の袋を貰うと長生きする.
3. The
official manual/booklet that came with CV2 FDS doesn't disclose the name of the Strigoi graveyard man. CV2 FDS guidebooks/walkthroughs sold in Japan refer to the Strigoi graveyard man as "gypsy".
4. Bisqwit
provided insight into the aspects of this term/word some time ago, with some such information about it referring to "waddling policemen" (slang term) -- but flat out admits it may not be true (with relevance to the character in CV2). Konami said ahiru (duck/animal) and they meant ahiru (duck/animal).
5. It just so happens that the same graphics are used for the ferryboat man. This is almost certainly due to CHR space limitations.
6. The reason CV2 is filled with lies and other deceitful stuff is because at the time it was incredibly common for game developers/publishers to put in weird misleading "clues" solely to get the player to purchase a strategy guide. The deceitful townsfolk are in both the English and Japanese releases of CV2. But the "duck" line is accurately translated either way.
7. I've read
speculative crap about it being some kind of "inner-Konami joke". That's generally nonsense -- but what
is true is that ducks in Castlevania games since then have been a running joke.
In other words: all this hullabaloo about the "graveyard duck" and "what is it?! IS IT SOME SECRET? MY OCD IS KILLING ME!" certainly has Konami laughing still to this day (and probably why they keep the duck references ongoing -- I know if I worked there I'd keep it ongoing just to see to what degree the Internet would take it; we're bordering on alien conspiracy theory levels). This isn't some weird quirky "mistranslation" like in Zelda 2 (the whole Bug / Error joke). Occam's razor, folks -- look it up.