''You're Going to Die, Charlie''
For this you must defeat a goblin called Charlie in the Orobus Fjords. He is located near the Yggdrasil tree which is south of where you enter the area. You will have to talk to this tree for a quest to collect seeds, and the tree will ask you to kill Charile, just stand on a rock and kill him with a bow.
And as Lil Miss Cherry has added, to which I was completely unaware:
"Also recommend mind reading him before you kill him as a malachite gem will spawn in his chest just up the ladder in the tree top if you do."