How it all started
With most twins or siblings in mythologies, we could always assume that one is evil and the other one is good. The same can be said between Glooskap and Malsum from the Wabanaki Native American Mythology. Here is one of the many stories of them:
Before the earth is how it is today, there existed greater beings who made it how it is. They were Glooskap and Malsum born by the great Earth Mother. It was said she died by Malsum who was born after Glooskap by tearing through her belly. Just like how Ahriman did in the Zoroastrian Mythology.
The creation of Earth
So, in honor of her, Glooskap created plants, animals and humans from her body while Malsum made poisonous plants and poisonous animals… Probably thinking of the ecosystem and balance but he’s definitely evil because he wants to kill Glooskap.
Now, why did Malsum wanted to kill Glooskap? Because he was getting bored and its his idea of fun.
So while plotting, Malsum kept saying that they’re both invincible and asked for his good brother’s vulnerability. Because it would be useless if he even attempts to kill the brother when he knows its impossible.
So, Malsum kept badgering for his weakness that he even told Glooskap his own. Which is the roots of the fern plant, apparently.
So Glooskap finally gave in and since he knows the brother would kill him, he said he can be killed with an owl feather. Without delay, Malsum just went and obtained an owl feather and used it to kill Glooskap.
But little did Malsum know that it is a weakness but not enough to be killed, it probably worked like the potion that Juliet drank in Romeo and Juliet that Glooskap was just deadly unconscious but was able to be resurrected.
Now knowing 100% that the brother really wanted him dead just like how he killed their mother, as a precaution he has to kill would be killed again.
Then remembering Malsum’s confession about the fern root weakness, Glooskap pulled a fern plant out and flung it at Malsum who surprisingly didn’t lie that it was really his weakness. So Malsum died leaving a malevolent wolf spirit in his stead.