Before you deal with Rezakiri and Shrowd Behemoths in Dauntless, you must fulfill a series of requirements. The first one is to reach Slayer Level 20. If you not reach at least this level then you cannot take these monsters. Besides, another important requisite is that you must have completed all Level 4 missions in the game. If you get stuck in these missions, you can get some help from your friends.
After fulfilling these two requirements, you can start playing two weekly missions. In one of them you have to deal with Rezakiri or Shrowd, and in the other, you will encounter the other Behemoth that you have not yet faced. But this one will be accompanied by another one, selected in a random way to make things a little more interesting.
In Dauntless, there are nineteen Behemoths that you must face in order to advance in the game. The type of rewards you’ll get will depend on the type of monster that you face. For ex: if you want to get Neutral Orbs then you'll have to look for them where there is a neutral type Behemoth. Depending on the type of monster you face you will need one piece of equipment or another but if you want to advance in Dauntless you’ll have to face all types of Behemoths as soon as possible.
Check out our strategy guide on how to defeat Behemoths easily in Dauntless. This guide covers tactics and weakness of Behemoths in the game.