What is the purpose of で in this sentence?


I am currently reading [chapter 118 of the webcomic One-Punch
Man](http://galaxyheavyblow.web.fc2.com/fc2-imageviewer/?aid=1&iid=119), and
came across this sentence:

> 検定の日を狙っていた奴がダメ押しでもう一人現れた.

I run across a lot of sentences with the particle で, and I never know when
it's supposed to be used as "and" when it's used together with a noun, or
"because". I don't know if this sentence is "(the person) made doubly sure,
AND..." or if it is "BECAUSE (the person) made doubly sure, ...." or maybe it
means something completely different.

Is there a rule or hint I can use to rule out one or the other?

**Edit:**

So I asked A Japanese lady I tutor in English, and she said that this is a
really weird grammar structure that mostly youth use, and seems to be kinda
limited to be used only in Manga (unsure how genuine this is), but the meaning
of the で particle here is connected to ダメ押し, meaning that the person who
came/aimed at this test came here by being absolutely /doubly sure in their
heart that they would win/pass, and it connects to もう一人現れた by meaning that
another person who was absolutely/doubly sure they would win/pass in their
heart also arrived.

Now I probably paraphrased this horribly, but at least now I know that it was
neither of the ways of using the particles that I previously thought, and I
can use that information to research it more on my own.




I understand the sentence now. I was unable to articulate her explanation of
the で particle's function in my edit. I've been looking in textbooks. but I
can't find any function that explains her understanding of the particle here.
some example sentences she wrote me:

  1. トムは必死「で」帰国の準備をしています。- 必死「で」-> 必死「に」でもどちらでも同じ意味になります。 
  2. 私はトムが帰ってしまうので暗い気持ち「で」過ごしています。-> 暗い気持ち「に」とは、言いません。暗い気持ち「で」だけです。 

Consider it answered.




I think this time it is used as "and" since the second part is "another person
appears"

I don't really know if there's a rule or not, but personally for me, if I am
unsure then I just remove the で and see if the part before and the part after
it make complete sentences that make sense.

Not sure if this helps.

