How can i make some great plot twists in my fantasy story?

I'm now wiriting my fantasy story and i was struggling on how to add some plot twists to it. Like for example, i had one of my main characters depart from my protagonist's group in order to search for the leader of the Hakeron Clan( in case my story is going to be a sequel) and the protagonist and his group are on their own, but however i tried to add some mystery to the character's departure, but i've keep messing up. Please give me some examples of how to make plot twists.