What is the meaning of じゃぞう

Question

せっかくのベッピンさんが台無しじゃぞう

This sentence is said by an elder character on Mirai Nikki episode 6.

I understand that じゃ is an old way of saying だ but what about ぞう？Is that some kind of 終助詞？

Could that be a misspelling of ぞ？

Answer 1

Yes, it is the 終助詞 ぞ. And not a misspelling, but a common way to spell its elongated pronunciation (elongation stands for emphasis, btw).

Because of the overwhelming majority of existing words with long vowel ō being spelled with おう, many people find it intuitive to write ō that way, even as phonetic transcription without etymology. A illustrative example is:

おかあさん okāsan "mom"
おにいさん onīsan "(big) bro"
おねえさん onēsan "(big) sis"

but:

おとうさん otōsan "dad"

The example above is already orthographically fixed, but in this case you can choose to use ぞお, ぞー, ぞ～ (or even ぞ〰) instead, and it is perfectly fine (though with subtly different nuances). It applies to other particles and interjections that end in o as well.

よ → よお/よう etc.
ほお/ほう etc.
のお/のう etc.
おお/おう etc. (but in the exclamation sense we usually stick to おお)
（早くし）ろ → ろお/ろう etc.