The last five nightfalls I have done I have received only 8-12 ascendant energy each time
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Things could be worse. You could have received ascendant shards.
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I keep getting coiled hiss for some reason.
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It's just luck of the rng. I received the weapon "up for anything" with the same perks 5 times in a row. So I feel your pain but alas I just carry on busting baddies in hopes of something else.