The Festering Fang Quest Guide

To start the quest, you have to get a strange tooth from one of the 4 locations. You can start by going to the red cave like area in Wyrmrest Valley. Close to the center of the area, there is a "strange tooth" that you can pick up. Take the item and you will be asked to go back to the camp to ask for more information.

To get to the cave with the red heart, start by teleporting to the closest teleport waypoint. Head north and drop down to the area in front about 3 times, until you reach the area where the bones start to stick out, then turn around to enter the cave.

For the one in the upper right, the strange tooth is in a small island in between Dragonspine mountain and south of Springvale. It's inside a frozen ice, so you will have to use a scarlet quartz that can be found in the marked area shown above.

The second strange tooth location is marked on the map. You can see some bones sticking out of the floor. Get close to it and interact with the things that you can "interact" with to be able to pick up the strange tooth.

The third location down south east is in a frost lawachurl area. You might have to defeat it to be able to pick it up. Use the scarlet quartzes scattered around for an advantage in the fight.

After getting 50 Starsilvers, head back to the smith at the camp, and you will be asked to go back to the heart. When you get there, 3 Fatuis will show up (Electro, Geo, and Pyro). Make sure that you bring the required elements to help take down their shields. Otherwise, keep using the scarlet quartz that's available in the area.

Interact with the Heart after you defeat the 3 fatuis, and you will be ambushed by 8 more fatuis, that come in waves. To make things easier, it is highly encouraged to bring a Pyro, Cryo, and Hydro characters. The scarlet quartz lying around in the area can help, but it will still be a slow progress if you don't use the proper elements.
1st wave fatuis: 1 Cryo and Electro
2nd wave fatuis: 1 Cryo and 2 Geo
3rd wave fatuis: 1 Electro, 1 Pyro, and 1 Geo

Head back to the smith, Orban, and hand over the required materials to craft the spear to finish the quest.

Finishing the quest will award you with the crafted weapon: Dragonspine Spear, the blueprint to craft the Dragonspine spear, and an achievement "Dragonspear" in the "Visitors on the Icy Mountain" category.

The Dragonspine weapons have the same effects. It has a 60% chance at level 1 refinement to deal additional damage by dropping an ice, damage is increased further if the enemy is affected by Cryo. The dropped ice deals physical damage, and does not apply Cryo to the enemy.

Once you get the blueprint, you can now freely craft the Dragonspear, but you will need 8 Vitalized Dragontooth. To get this, you will have to pick up the Dragontooths from the same 4 locations again, then bring it back to the red heart. Submitting 4 Dragontooths will give you 4 Vitalized Dragontooth. The Dragontooths will respawn again in the same 4 location within a few days(?).