As a Slayer, you will have to know which weapon is used to slain the numerous behemoths of the Dauntless world and hope winning your hunt. Each element has a weakness and you will have to get the weapon of the opposite element to inflict the most damage.
The armor is also important and contrary to the weapon, it will have to be of the same element as the Behemoth to be strong. We break everything down here.
Table
Example
When you come into the lobby before the hunt, you will access the "Hunt Info" tab. You will see here what are the weaknesses of the behemoth which is being hunted down.
Regarding neutral behemoths, you won't need particular stuff. You won't have damage bonuses nor elemental stuff. As for neutral armors and weapons, it's the same. You won't get bonus/malus in the fight. The game also shows the threat level with a calculation based on the currently equipped stuff.
In Dauntless, there are some atypical quests called Patrols, which will allow you to loot a lot of rewards (orbs, rams, Dull Arcstone, Shining Arcstone, etc.) weekly or monthly.
