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Can I still get Dauntless Delver if I use the emergency revive?



You can get this achievement with party members but they have to not die also (if they want the dauntless d,) Or you could try soloing. I do not know if using emergency revs count as I have got my achievement last year, but I would assume it does because that counts as dying.

I actually got dauntless delver on elite, but I had someone help me near the end. They were a stranger no less, and died a few times for me, which was both sweet and a lifesaver (because stratum 6 compounds are so awful).
The achievement is still very possible, but I'm 99.9% sure you can't use your ER.

I attempted to get that achievement, used an ER at D20, reached the core and I haven't received this achievement.

You must make it through without using your ER at all.
It's a nice achievement to have. Since you asked you must be going for it.
Good luck.