A Japanese and Italian question

While looking at a comic written in Japanese, I ran across the line ドルチェッティ、オ スケルツェッティ！ From the context I figured that it almost had to be "trick or treat," and since it wasn't the English phrase but the character speaking might use Italian, I found via googling the Italian phrase "dolcetto o scherzetto." Problem solved! Now I just want to satisfy my curiosity.

Japanese: How would you romanize ドルチェッティ、オ スケルツェッティ? I'm guessing something along the lines of "doruchetti, o sukerutsetti," but I haven't had much experience with this sort of thing.

Italian: I assume that the person writing the comic wanted "dolcetto o scherzetto," so I find it odd that the Japanese ends with an i instead of an o. Not knowing any Italian, I have an instinct that says the i ending might mean it's plural in Italian. Did google lead me astray, and is the Italian for "trick or treat" slightly different? Or did they write something like "tricks or treats" in Italian instead? Or some other explanation entirely?

Thanks for any insight you can share!