I brushed up my rusty pixel art skills and created two placeholder monster sprites. The angel looks pretty cute already, but the imp needs some work.
Angel
Magical creatures of pure good. They strictly adhere to the moral rules written in their "Holy Codex" which encompass pureness, chastity, humility, abstinence, kindness and peacefulness. The last one with one notable exception: Anyone who does not adhere to the rules of the Codex is considered a sinner, and sinners must be opposed with all means necessary. Destroying the sin is a cause which justifies all means necessary. The angels prefer to make a sinner repent and abandon their sinful ways, but when this turns out to be a futile attempt, they often decide to destroy the sin by destroying the sinner.At first, other creatures usually consider the berating of the angels about their "sinful ways" amusing at best and annoying at worst. But it is foolish to not take them seriously. Angels are not allowed to bluff or lie. When they say that your adherence to a sinful life will have "dread consequences", they mean it.
Angels are also intelligent, educated, organized, polite and well-spoken. As the self-proclaimed moral guardians of the kingdom, they are very interested in politics. The angels openly trusting someone has a very positive influence on the public opinion. That's why many politicians employ some angels as officials for image reasons. Besides, they are smart, diligent, hard-working and frequently even work for free. Unfortunately, closeness to the angels has the disadvantage that any "dirty business" must be hidden from them at all cost, because they will not hesitate to make it public, abandon you, or even outright attack you when they doubt your moral integrity.
Fallen Angel
An angel which willingly commits a sin, or which enjoys performing a sinful act when forced to do it, immediately transforms into a fallen angel. In contrast to angels, they are hedonist creatures whose only concern is their own well-being. They only cooperate with others as long as it gives them direct gain or pleasure, and they will abandon any ties to others as soon as they become a burden. That's why most fallen angels are solitary creatures.Ironically, they are often less dangerous than their good counterparts. They don't care much about the business of others, unless it directly interferes with them. Although fallen angels do not hesitate to use violence to get what they want, they will usually back off when the resistance they have to bother with outweighs the potential gain.
But still, when there is something they really want, they will not have any moral qualms about using any means necessary to get it. There is also a faction of fallen angels which can indeed be very dangerous: Those who discovered the pleasures of sadism and domination. A fallen angel who enjoys to cause suffering is someone you don't want to meet.
Imp
These evil creatures strive on the hate and anger of other creatures. They need hate of others to survive. When nobody hates an imp, they starve to death. To get people to be angry on them they will use insults, practical jokes or even violence. They can be considered the "bullies" of the kingdom. Fortunately, they are small and not very powerful, so they are more of a nuisance than a real threat. But being a nuisance is a skill they trained to perfection.The best way to deal with them is either by ignoring them, or by trying to have a positive attitude towards them. While hate of others is food for them, affection is pure poison and will drive them away. Considering them cute, feeling sorry for them that they must be mean to survive or believing that they are really nice beneath their outer shell is a sure way to drive them away.
