During my playthrough of Persona 5 I’ve come across んばかりに once and んとする many times. It just depends on the material, I suppose 
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Ah, interesting - I’m guessing it is 役割語 when you’ve seen it then? I mostly just read regular novels and watch YouTube or variety shows (also I live here) - it does show how different the language can be depending on what you consume though.
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Now that you mention it, I remember reading about this in the んばかりに N1 grammar point in BunPro:
The caution section says:
Also, related to the funny video you posted, I remember that ねば (the classical way of saying なければ) from this N2 grammar point:
It’s interesting to see how this seemingly archaic way of speaking is still being used in some regions (秋田県 in this case) of Japan. Another example of how these way of speaking are judged based on experience.
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