Secret Archetype: Gunslinger
You have to kill two world bosses in the game, then you get an engram. There are more world bosses, as you progress through the story you will encounter several world bosses.
If you come (to Mudtooth) after one boss, for example, you get a ring. If you go (to Mudtooth) after the other one, you get the rest of the rewards.
You have to use all the dialogue you can think of Mudtooth, listen to all the stories (10+ times).
Hopefully, it’ll help!