Spoiler Alert: WARNING! This page happens to contain a lot of heavy spoilers that are all originated from the Overlord author, Kugane Maruyama and his collection of written works. Anime-only watchers and Manga-only readers, please take some time off to reflect it over for a bit before choosing to expose yourself on reading the information below recklessly.
This page shows a list of racial classes appearing from YGGDRASIL and the New World throughout the Overlord series.
In the context of YGGDRASIL, every demihuman and heteromorphic race but humanoids are allowed to unlock racial features. This, in turn, gives players racial characteristics ranging from monstrous appearances, abilities, skills, resistances, etc. when they reached certain levels. Particularly, it was heteromorphic monsters that had the highest amount to gain such as stats through racial classes but can still have levels in job classes nevertheless. Second to them was demihumans who are fairly balanced between both racial and job classes combined. Because of that, certain heteromorphic creatures tend to possess multiple forms as a result of investing levels in their racial classes.
However, it was considered troublesome to waste time to level up heteromorphic racial classes, because they usually become the targets for PKing by other players. Moreover, there was still a limit to how far the benefit of racial classes goes especially its resistance. For instance, even if a heteromorphic character combined their racial resistances with job classes that granted resistances, it is impossible to resist all elemental attacks even with enough preparations in doing so. According to Maruyama, if any more racial classes over 45 levels are taken, one of the classes in possession by the character will disappear. This only applies to the Web Novel, however.
On the other hand, they are inflicted by racial penalties and weaknesses based on the kind of races the characters are playing. For starters, beings like Zern could be negatively affected by race-specific spells when used against them. Aside from that, there are some magic items with racial restrictions over who can use them. They can also be penalized or restricted from entering certain areas such as cities where it contains other races like humanoids.
Despite the setbacks of having levels in said races, they were still highly regarded as popular among players. Their source of popularity stems from how they are able to endow in different forms and stages of evolution like final bosses in a game. In addition to that, people were fond of how these heteromorphic beings were weaker in their human and demihuman forms, but more powerful in their fully monstrous forms.
Overall, regardless of their differences, what heteromorphic and demihuman monsters have in common is that they possessed superior physical abilities than regular humanoids. As a matter of fact, they are able to acquire strong racial skills at higher levels. Still, heteromorphs are unique entities who get to acquire monster-type special skills that demi-humans couldn't obtain. Demi-humans, on the other hand, possessed a racial skill related to things such as damage resistance.
Just like their job class counterpart, every racial class had a maximum of 15 levels to invest in. They're commonly ranked between either base, high and rare. Base job classes can only be leveled up to 15, high classes meanwhile can be leveled up to 10, and finally rare classes like Overlord, a high-tier race can be leveled up to 5 at max. Naturally, as the class level grows over time, the stronger the class ability that is obtained.
The author Maruyama notes that Dragons in YGGDRASIL are unplayable, but players can still invest levels in upright races that closely resembled dragons.
According to Maruyama, every racial class had several standard appearances. In what way it was altered, depending on the tenacity of the person in question regarding their aesthetic sense. Therefore, one can actually make an exterior resembling an Eight-Edge Assassin if they feel the need to.
In the New World, it was viewed that creatures with racial advantages generally are not inclined towards training. Though there are some of them who would put in the effort and time to pick up such skills, and that made them very difficult opponents.
At present, dragons from the New World in their growth stages are contributing less to racial classes and learning more favorably towards job classes instead.
Despite being a dungeon full of heteromorphic monsters, most of Nazarick's denizens by far seemingly have more levels in job classes than their racial classes as shown on each of their respective character sheets.
There are different sort of items like Book of the Dead which gives the person using it an option to change their race. In the game YGGDRASIL, it was possible to change race mid-way that can most likely affect their racial classes afterward to the point of receiving losses and gains thereafter. To do so though meant not only requiring the item, but also had to have the following prerequisite racial levels, skills, have a minimum level of types of levels, and perform a certain event.