Dante doesn't say this in the original Japanese version of the DMC2 novel.
The official localizations of the novels are pretty bad...
I can't even call some stuff 'mistranslations' because, just like in the case of this part from the DMC2 novel, it's something that was inserted by the translator.
It's unfortunate. When people want to use stuff from the English novels and the DMC3 manga in their discussions, most likely they are presenting fan-fiction. How else can I describe when sometimes there's nothing in common with the original dialogue/ text? Or they have added extra things for no reason, especially with pretty straightforward dialogues?
So yeah, let's look at what the original text says:
魔王と対峙するダンテの目には いささかの遠巡も、そして迷いもない 。
「おねんねの時間だぜ、ムンドゥス!」
その軽口もまた、まった＜損なわれる気配はない。
Translation: Dante stood before the Demon Emperor, his eyes showing no hint of hesitation or uncertainty.
"It's past your bedtime, Mundus!" (yeah, I used the line from DMC5)
Even now, his wisecracking attitude was still strong." (another tl: Even in this moment, he didn't hold back on the wisecracks.)
That's it. The translator made that up. Just look at how the sentence is constructed. They made Dante have a inner monologue which you can see it's not there.
The bolded line is the narrator making who made a remark.
Also, from the original text, you can tell that Dante was making fun of Mundus, talking down to him, because おねんね means bedtime, but it's how you would say it to a child, so it would be something like "nighty-nighty", hence why the original mentions his 'wisecrack attitude' I used the line from DMC5 "it's past your bedtime" to show how else it could be translated.
I would also like to mention that I'm not looking forward to Netflix DMC and I will say that personally, I do not like what Dante said in the recent trailer...
Like WTF? If that will happen more times, I think it's stupid. Dante always said his one liners and did other goofy stuff with confidence. When did he act like "oh yeah, that was so cool of me." or 'let me try again'.?
Hopefully he only said that just to calm that woman. If he's gonna taunt enemies, I hope he won't always be like that, , saying stuff like "Nah, that's wasn't great". "It sounded better in my head"
So, if you're gonna tell me or others that he has done that before and it's this part from the DMC2 novel that's supposed to be proof...Well, I hope my explanation made you see that localization made up that part, which is something that I don't support when it comes to making translations.