Dauntless presents its players with a shattered world in which monstrous Behemoths reign supreme: the only sensible thing to do, really, is to go out, slaughter these creatures, and make weapons and armour out of their body parts. Nightbringer Rift Spike is one such part.
Dauntless Nightbringer Rift Spike is a commonly-dropped crafting item that players can find after killing Riftstalker-type Behemoths, usually found around The Maelstrom. You'll find all you need to know about Riftstalkers down below.
Where to find Nightbringer Rift Spike in Dauntless?
As we mentioned above, Nightbringer Riftspikes are a common Reagent in Dauntless, which means they are used to craft weapons, armour, and consumables of various kinds. Riftspikes, in particular, drop from the nasty Riftstalker Behemoth - an Umbral creature that is weak to Radiant attacks and weaponry.
To farm Nightbringer Riftspikes, visit The Maelstrom and hunt these beasts down there. Spikes drop from Riftstalker tails, so cut those off wherever possible. Be sure to take equipment that can reliably interrupt enemy attacks, because the Riftstalker will otherwise keep jumping in and out of portals and flanking you with ease.
We've also got similar Dauntless guides on Pristine Moonfeather and Conductive Shockspine crafting items, which you should definitely reference when necessary. A more generally-applicable guide would be our Dauntless Element chart, that you can download and use to quickly figure out what element works best against which boss. In any case, happy hunting!