With the exciting discovery of not one, but two new Pokemon Types in Crater Region this past Starfall, Eden Labs is excited to reveal what we've learned about the appearance of Void Pokemon and what you can expect to see when encountering them! Eden Labs was able to capture this particular subject, a Ghastly we have come to name "Petrichor". Petrichor shows a variety of features typically found on Void Pokemon.
Most of these are features the Void Pokemon CAN have, but most aren't REQUIRED! The main requirements are that the Pokemon must be solid black/on a black-dark grey color palette, and they will always have red eyes when you first encounter them.
Void-Types can present:
Void-Type Pokemon are the only Pokemon in Crater at this time that can be solid black with no other markings.
All wild Void Pokemon have red eyes of some variety. However, after having been captured, many Void Pokemon eye colors can change to any of the regular eye colors found in Pokemon! They can be purple, yellow, blue, green, and more.
Red and yellow are the only additional colors Void pokemon can have, and black/dark grey can be the only base color.
They can have spikes and horns whether they're simple like on Petrichor, or far more elaborate. The spikes can be solid, gradient, have red tips, be solid red, or they can be yellow instead, or a combination of red and yellow
There will never be a Void pokemon that is a base color of red with black accents, and so on.
Void Pokemon can also have extra sets of actual eyes, but no more than one pair of extra limbs.
If they have extra sets of physical eyes, the additional sets WILL ALWAYS REMAIN RED permanently. The extra limbs also need to be a duplication of what the pokémon naturally have. It can't have wings if it originally doesn't have any.
After they've been caught, you can choose whether they keep the red eyes, or settle on more normal colors.
Here are some examples of Void Pokemon eyes found in the wild:

This is a classic Cross-Pupil Void eye. They are the most commonly encountered by Eden Labs associates.

This is a non-cross pupil Void eye:

And this is a pupil-less Void eye:

Void Pokemon can also retain their cross-pupils even after the eye color changes, but in this case the pupil ALWAYS REMAINS YELLOW.
Here is an example of a Void Pokemon whose eye turned purple, but retained the Cross-Pupil