The more Behemoths you slay in Dauntless, the closer you get to doing battle with their Heroic versions which significantly up the challenge. They're also the sources of reagents like the hellstone shard.
Here's what you need to know about getting your hands on the hellstone shard reagent in Dauntless to upgrade and craft new gear for your Slayer.
Dauntless Hellstone Shard
If you're after the hellstone shard reagent, you'll have to go against the Scorchstone Hellion, one of Dauntless' particularly challenging Heroic Behemoths.
You're going to have to slay the Scorchstone Hellion for a chance at getting hellstone shards and, as usual, breaking off parts can reward you with more of the reagents. Pursuits for this particular Behemoth are unlocked after completing the Shared Sacrifices quest.
You might want to bring a handful of other Slayers into the fight and coordinate to take the Behemoth down. As with other beasties in Dauntless, the Schorchstone Hellion has its own strengths and weaknesses. When going for that hellstone shard be sure to equip fire resistant armor and a weapon imbued with the frost element.