Note: While it's generally considered good practice to do so, it's not required for an artist to follow these rules when posting on e621.

From the Furry Fandom wiki and Protogen Guide image:

Protogen exist in three tier'd variants:

• Common (1): The standard Protogen. These have two ears. Free to make.
• Uncommon (2): These Protogen have two pairs of ears and a pair of horns horns (five variants available). Free to make.
• Rare (3): These Protogen have three pairs of ears and can have multiple additional limbs, including extra tails and wings. Must be bought (citation needed).

As a sub-species of the Primagen, Protogen have limitations on what they are able to have as a species when being created. When creating a Protogen, the following rules must be observed:

• Protogen must not have any dinosaur traits/anatomy.
• Protogen must have biological ears.
• Protogen must have the short, round visor.
• Protogen can only be bipedal with no feral forms or hybrid fusions allowed.
• Protogen are not allowed to have wings unless they are of the rare variant.

Protogen Tails are easily swapped and replaced, but there are six standard designs availible:

• Standard Top Cover: Resembling that of an eastern dragon, this long tail is slightly chubby at its base and is scaled along the bottom ~half with mid-length fluffy fur cascading across the top half. Can be either fur-tipped or scale-tipped.
• Long Full: A basic fluffy tail.
• Long Banded: Similar to the Long Full but with 1-3 furless bands of tech, typically near the end of the tail.
• Short Nub: Visually similar to a cottontail.
• Tech Nub: Identical in length to the Short Nub but all slightly-mobile tech.
• Aquatic: A fully-tech tail reminiscent of a shark tail.

There is no restriction of colour and pattern, but be mindful of others' designs and do not copy the palatte of a Primagen.