Angelicas are special powers bestowed upon chosen humans after the First Expungement. They are a paracausal force capable of interacting and damaging Ghosts — they are humanity's weapons.

(WARNING: Mild spoilers below)

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Angelicas revealed in the story so far (chronological order):

Stormbringer - Power to conjure storms, thunder, lightning, and rain. It is one of the Four Elemental Angelicas, able to control electricity and arc energy. The Four Elemental Angelicas are all commonly found, with Stormbringer being the most common.

Oculus - Power of eyes, from seeing through walls to detecting hostiles on a radar within the user's mind. There are four main branches of this Angelica: Eye of Omnipotence (seeing through walls, invisible entities and clues, etc.), Eye of Twilight (enhances eyesight range, clarity, focus, etc.), Eye of Paracausa (detecting other Angelicas), and the lost Eye of Epitaph (???).

Blacksmith - Power to enchant normal weapons with paracausal energy, allowing them to injure Ghosts. Wielders of this Angelica also usually have higher physical strength than the norm, due to spending a lot of time performing tedious, laborious tasks with heavy tools and machinery.

Daredevil - Power of pushing human physical limits, mainly in speed and agility but not strength. Wielders of this Angelica are usually... well, daredevils.

Starsinger - Power of the stars. Highly destructive and difficult to control. Despite being a rare Angelica already, only a select few of its wielders are able to use this power properly and even fewer are able to use it to its maximum potential. Requires innate talent and lots, lots of practice. Also, highly RNG-based.

Shapeshifter - Exactly what the name suggests, users of this Angelica can morph themselves into any object they can see and feel. More skilled users can morph without there having to be the object right in front of them. Shapeshifters can shift into other living beings like animals, people, and even Ghosts, but will only gain their appearance, not their powers due to the extreme complexity of the process. Finn, for example, cannot gain eyesight by morphing into someone else because he himself does not possess the ability to see.