This page or section includes possible gameplay spoilers or secrets. Tread carefully.
A Halo can be obtained in each run. Obtaining it will grant a piece in the Achievement Pillars.
Collecting a halo will provide 10% fire-resistance.
There are 2 types of halo, light and dark, and only one can be obtained at a time.
They will appear if you collect enough perks of the right types to have a 'score' in that type of (+/-) 3 or more. You start with a halo value of 0, and each +1/-1 perk moves that value. So if you have a +6 halo value and take a -1 perk, you won't lose the Light Halo.
You will lose the halo if the score drops outside of the target score, but if there is no limit to re-obtaining either halo.