Oasis (quest)

Oasis is a Fallout 3 quest. It is also an Xbox 360 and PC achievement.

Objectives and walkthrough
Harold, a special FEV mutant with a tree on his head which he called Bob, eventually found himself overwhelmed by it and became rooted to the ground during his travels in the Capital Wasteland region. Here he was discovered by several people who began to worship him as a god, and a small and exclusive cult known as the Treeminders began to form in secrecy. Bob began to blossom and many plants grew in this area, which became green with life, a stark contrast to the outer wasteland.

Harold reveals his true identity, and begs for mercy; after being stuck in the same position for decades he is eager for death. The other dwellers of "Oasis" have ignored Harold's wishes so far, and ask you to instead either suppress or expand Harold/Bob's fertility.

Birch gives you his liniment that will cease Harold's growth, and Laurel gives you her liniment that will increase Harold's growth. Entry to the cave system is gained from the main Oasis hub area, not the doorway within the same area as Harold.

Once you enter the cave you have to navigate through, there are 2 Mirelurks, and a Mirelurk King. Once you get to the room with the large irradiated pool of water, you will have to swim underwater to find the passage to move onward. There will be 2 more Mirelurks and a Radroach. There's a door further down the cave. After you go through the door, there are a few more Mirelurks. A pathway off to the left near the door has a small alcove where someone used to live. Their skeleton is still there, surrounded by loot - including a pre-war book, D.C. Science book, and Silenced 10mm Pistol. Further on you'll hear a thumping sound. The thumping sound is Harold's heart, apply the liniment of your choice and then leave. There are 2 ways out; one through a door in the room, which leads to a room with 2 more Mirelurks and a Mirelurk King that are very close together as well as another irradiated pool of water you will have to swim into to escape, or you can back track the way you came.

Help Harold grow
After you apply Laurel's Liniment, leave the caves and you will find Laurel near Harold. Harold will accept that the people need him and thanks the Vault Dweller. Laurel tells you that Bloomseer Poplar, Sapling Yew, and Branchtender Linden have gifts for you. Branchtender Linden offers you Linden's Outcast Power Armor, ¹Sapling Yew offers you Yew's Bear Charm, and Bloomseer Poplar offers you Poplar's Hood

Harold also has some more dialogue about your choice, if you choose to speak to him.

¹After doing this, I didn't receive Yew's Bear Charm. Perhaps it's a random reward or you need to succeed on the Speech Challenge when you talk to her

Stop Harold's growth
Branchtender Cypress gives you: 2 Missiles.

Branchtender Maple gives you: Maple's Garb (DR 12, Agility +1, Perception +1)

Note: I had a bug in which Maple didn't give me anything. She greeted me in a friendly way, but I didn't have the option to ask her about the gift.

Kill Harold
There are two ways to kill Harold:

Burning him: If you burn Harold, then you will lose some karma and the dwellers will become hostile.

Destroying his heart: Destroying Harold's heart gives you the Barkskin Perk (5% damage resistance). You will also gain Yew's Bear Charm after speaking with her (this likely requires succeeding on the Speech challenge or using the Child at Heart perk when you first speak to her.)

Bugs

 * Telling Fawkes to wait in the cave while the PC completes the quest may divide the game by zero when the player attempts to reenter the cave.