Well, there's some point missing here... Beldr (that's the God's name) was a blessed child. The day he was born, his mother forced each living thing to swear an oath, in which they promised to never harmed him, and she just forgot Holly (that's how you call it ?). Loki, who was jealous of all the attention given to this new god, made an arrow out of a branch of Holly, and gave it to the brother of Beldr (who was blind, important detail). The brother shot the arrow, guided by Loki, and the arrow killed Beldr. For punishment, Loki was chained and tortured like said before (venom from a giant snake that burns his forehead, etc. etc.)