Wormbrain is a goblin in the Port Sarim Jail that players must barter with in order to get the third piece of the map in the Dragon Slayer quest. One can offer him 10,000 coins for his map piece, or fight him. When the player reduces him to 0 life points, he simply drops his part of the map and says, "Ow!". Players must then use Telekinetic Grab to get the map part (3).
Wormbrain, along with a small band of Goblins, decided to ransack Lumbridge. He and other goblins forced Lachtopher to flee to the other side of the River Lum. Then they came forth and killed Lozar, an elderly mage and the second last surviving Crandorian. After that Wormbrain found a box which he tried to open. Then the others left Wormbrain to the guards and fled.
Originally in Dragon Slayer players had no choice but to kill Wormbrain and use Telekinetic Grab to get the map piece.
When his life points get to zero, you will receive a message that says, "You have just beaten Wormbrain up. Give the poor goblin a break".
If you have obtained the map piece during Dragon Slayer, trying to attack him afterwards yields the message, "You have already taken Wormbrain's map piece. There is no use in beating him up further." even if the player obtained the map piece by paying 10,000 gold coins.