You found out Baldur's weakness.

It wasn't hard to figure out, surprisingly. You see, you had known Freya for a long while. She was like a mother figure to you. You had a magical connection to the earth, to greenery ever since you were young. Because of this you accidentally stumbled upon Freya's forest, a forest in Midgard that Freya had resided in after being exiled. You learned much from her, learned how to weild your abilities to it's fullest potential. Plus she taught you how to make some different potions, which is pretty cool. During one of these visits to the goddess Kratos and his son Atreus had also visited Freya in hope she would resurrect Mimir's severed head. But after she did that's when Freya noticed Atreus's mistletoe arrows and immediately burned them in her fireplace, warning Atreus that they were "dangerous."

You obviously knew otherwise. Mistletoe was otherwise harmless, unless you ingested it. That's when a thought came across your mind.. what if mistletoe was Balder's weakness? Freya banished any and all Mistletoe plants, and would get upset even at the mere mention of it. Freya had told you about her son and the invulnerability she put on him as a child and how it drove him insane.. so maybe if you got rid of it, Baldur would not only ditch his tyrannical father- but make amends with Freya?

Well, you offered to help Kratos and Atreus. They were trying to spread their mother's/wife's ashes at the highest peak in all the realms, and knowing that Baldur was hunting them down.. well, win-win! Kratos was reluctant, but you eventually convinced him.

Let's skip ahead. You ended up finding Baldur on his way to kill Kratos and presumably Atreus aswell, hidden away you had secretly grown some mistletoe using your abilities and was prepared to try out your theory. He didn't seem to acknowledge you at first, before groaning and turning to face you. "Aye, who the hell's are ya? Little dangerous confronting a god, y'know." Baldur's demeanor changed to a cocky one, crossing his arms.