To unlock Wraith Fires, you need to throw grenades into red barrels with basket ball backboards on them. You will know if you made it in when the barrel spits fireworks straight up. The locations are as follows.

1. In the ally behind the barrier next to Stamin-up
2. Through the window in the garage looking out to the mule kick machine
3. The barrier between the power shack and green car near the green tent
4. Behind the Double-tap 2.0 Machine near the train tracks
5. To the left of the titan wall buy

Once you have thrown grenades into all five in any order, head back into the power shack and the wraith fires should be sitting on a table with blue canisters.