tl;dr: YES, you can use these bases- you just need to credit me and link back to the base for others to have access to. Also, I’d implore you to skim through the description here for some other info on the usage of the bases.
 
 

 
 
This is something I’ve been wanting to do for a little while stemming from my mentality from back when I was doing sprites, where I always wanted all of my little figures scaled accurately to size, haha! What I aimed for here was to create a viable tool that would be useful all around for designing Sonic characters in a variety of shapes and sizes- While also encouraging and reminding that I feel that “Sonic character” extends onto more than just the conventional Sonic-type Mobian base; Humans are also a vitally important part of the series lore also and a pretty central detail in especially the Adventure-era of games.
 
I made this in order for me to fast-track designing characters without needing to re-draw from scratch all the time when ultimately all I do is idle character designs and spend so much time trying to make them all consistent with one another, haha. This will alleviate more than half the trouble while still mentally keeping all my ideas together in the one spot. These bases are available for anyone to use freely, and I’ll offer some details on the creation process following. Here is the resources for easy grabbing:
 
 
Flats  
Base - Flat by Cylent-Nite
 
Flats + Transparency  
Base - Flat w/ Transparency by Cylent-Nite
 
Lineart  
Base - Lineart by Cylent-Nite
 
Lineart + Transparency  
Base - Lineart w/ Transparency by Cylent-Nite
 

 
From left to right:
 

 
 
Some tips for use:
 

 
 
[Sonic Expanse lore ramblings - Not necessary to read]
 
 
Anyways, just for a bit of fun, despite this being a general use tool I’m going to sprinkle in a bit of my own Sonic Expanse lore into this description lol. Most notably with regards to the biology of the species as according to the chosen figures here. So as per my Sonic Expanse world building, I go into particular detail with regards the creation of the world, as well as how Mobians and humanity came to be, with special focus on the subject of a natural layer of “Chaos Energy”. All throughout the physical universe Chaos Energy is present affecting nature and mutating it. On Earth it is most prevalent due to the presence of the seven Chaos Emeralds, with the Master Emerald resident to keep their powers in check.
 
 
Since the beginning of the physical manifestation of Earth (this has occurred numerous times due to the constant destruction and rebirths of the planet due to the Gaia Cycles), life on the planet evolves and comes into manifestation naturally, but where there are spots of large Chaos Energy buildup is where there is prominence in mutation and evolution. For the most part, regular animals are a rarity in present day, but they do still exist. A large portion of the animal population are present in a half-evolved state, which is the Mobini, or Animal Friends you’re all familiar with. They have acute humanoid sentience, capable of basic communication through mutters and chirps, however unlike their fully evolved Mobian counterparts, they are for the most part governed by animal instincts. As they possess some degree of Chaos Energy in-dwelling within them, this makes them a viable battery source for Dr Eggman’s Badnik creations.
 
Now as for the fully evolved “Mobians”, they are on a similar to equal sentient scale as human-life, enough to be considered their own separate branch of “humanity”. They, like the Mobini descend from evolution of animals through the exposure of Chaos Energy, however Mobians came into being from areas that possessed a much higher Chaos Energy output. Mobians are by far the most advance species on the Earth, though much smaller in numbers compared to the commonplace humans who preside over the present day world as the Fifth Great Civilization.
 
 
Human beings, in this world fall into place according to similar real world evolution theories- Humans evolved from a lifeform known as “Eosimias” (sonic.wikia.com/wiki/Eosimias), which is a primordial type entity that over time evolved into apes, and much later into the modern day conventional human. For the most part, humans are free from Chaos Energy mutation, however there are some unique cases where there is prominence of Chaos Energy in humans.
 
A few basic principles put in place in the Sonic Expanse world: Mobini and Mobians cannot breed despite similar evolutionary paths- This would be taboo for a Mobian and would be akin to bestiality in their sense. Relations between Mobians and Humans is possible and does occur from time to time all across the world, however due to the unconventional nature and differences between the species, in society it is considered strange. Breeding between Humans and Mobians on the other hand is impossible due to incompatible biology. However, there have been rare cases in history where cross-breeding has been possible, though this is due to Chaos Energy imbalances in one or more of the parents.
 
 
In modern day times, these Chaos Energy imbalances come in the form of the disease known as “NIDs”. In Expanse, NIDs is a condition where the sufferer is incompatible with the intake of Chaos Energy received from the natural layer surrounding the planet. It is toxic to them and makes them ill, which makes them susceptible to mutation and other mental and physical ailments. Professor Gerald studied his grandchildren, Warren and Maria, who were both afflicted with the condition and placed aboard the Space Colony ARK away from the Earth’s atmosphere in order to perpetuate an artificial space of Chaos Energy intake.
 
A similar occurrence of humans suffering from Chaos Energy mutation dates back to ancient times- back to the era of the Nocturnus Clan 4,000 years ago. During that time after the Knuckles Tribe’s defeat, the Nocturnus proceeded to dominate much of the world, enslaving all other species other than their own. In their conquest they met some resistance from human settlements that were exposed to heavy concentrations of Chaos Energy. These humans would over time evolve to be able to combat the technological prowess of the Nocturnus, having evolved to harness electromagnetic pulses to disarm the Nocturnus Clan’s advanced weaponry, rendering them useless against the defenders.
 
Gradualy, the Chaos Energy buildup would completely warp and transform the continent of these mutated humans, summoning it into the sky into it’s own planetoid hovering above the Earth’s surface hidden away from those who are a threat to it. With many centuries following, these humans would grow and evolve into a powerful mutant race known as the Zeti. They are a territorial band of tribal warriors, free from the rest of the world’s eyes- hidden away on their Lost Hex.
 
 
More rules of biology: Mobians and Zeti given their similar mutagenic evolved nature, are actually compatible for cross-breeding. However, due the the Zeti having been hidden away for the past 4 millennium this has yet to occur. With regards the rare cases where Humans and Mobians were able to procreate, this has been when the Human parent has been afflicted with an ailment similar to the modern day NIDs, and their biological structure has been altered to that of a similar state as a Mobian or Zeti. It is uncertain if there are any documented cases of Human-Mobian hybrids.
 
Zeti and Humans are no longer genetically compatible with one another for similar reasons as a Mobian-Human pair. However, the modern scientific workings of Professor Gerald have displayed results of suppressing the mutagentic factor in a Zeti subject known only as “Ms Anoe”, utilizing Artificial Chaos matter for ingestion in order to temporarily shift the Zeti’s biology, essentially making them “Human”. Due to the shutting down of the Space Colony ARK and the execution of Professor Gerald Robotnik, all traces of this research has been lost to history.