Chimera are beings made out of a substance called Energy, which is pure liquid magic.The very first chimera were born from the blood of gods, and over thousands of years of them reproducing and spreading across the universe, chimera became their own species divorced from their godly origins.
Chimera can still be born from godly blood, those are known as godshards and are rare, powerful, and gold like the blood they're made of. (and are quite proud of that)
Because they're essentially made out of pure magic, Chimera are extremely powerful magicians, but this comes at a cost: Any spell a chimera casts is from their own body, so a Chimera has to be very careful with casting spells, or they will die.
Chimera don't need to eat food like organic, non-energy beings. Rather, they gain energy from a source, which can be anything–an object, a location, an abstract concept, a piece of media...Anything that has lots of emotions and attention directed toward it can be used as a source!
But how do chimera feed off of a source? Chimera were originally born from gods, and modern chimera can still choose something they are the "god" of. Like gods, if some form of attention is given to the thing they're the "god" of, then they gain power and energy. If that thing they're the "god" of gets zero attention or is forgotten about, then no energy or power is given.
Chimera are very proficient shapeshifters due to being composed entirely of energy, and have a reputation for being tricksters who use their powers to mess with someone for the heck of it, or to give their source more attention.
TL;DR: Chimera are demigods with the ability to gain power from attention. They're the universe's biggest attention whores.
Chimera have a shifted and an unshifted form, their unshifted form being the closest thing to a default appearance. The true default appearance of a chimera is just a pile of energy goo with eyes, but it would be quite hard to move around and communicate as a pile of goop, so a chimera will have some sort of basic physical form they don't need to put much effort into creating to default to if they need to stop shapeshifting for whatever reason.
Energy itself is a glittery goop that can be any color aside from yellow/gold (unless it's a godshard), white (white energy is "dead" energy that is typically consumed to regain lost energy), and black (black energy is also "dead" energy, typically the color a chimera turns when it dies)
Chimera aren't perfect shapeshifters, and cutting one open will reveal that they completely lack organs. It's all energy inside, like a demented jelly donut.
A chimera's shifted form can look like anything, but chimera aren't perfect at replicating some things so there's usually something subtly off about their appearance. A chimera with the form of a human may have too many fingers, or unnaturally colored eyes, or perhaps they look exactly like an anime or cartoon character because that was their only point of reference when coming up with something. A constant tell for when someone's a chimera is to check the inside of their mouth: the inside of a chimera's mouth when shifted is pitch black, like starting into a void. You could also make a chimera bleed, revealing their shimmering energy for all to see.
This goes for other species too: a chimera trying to look like a normal cat might mess up along the way and give themself too many eyes, or a chimera trying to be a weird alien species that, has four arms will give themself a fifth so they can feel special or because they forgot that species only has four arms.
A chimera's appearance and personality reflect their source. Someone who used a pretty necklace as a source tends to look like the necklace, with physical features matching up with the necklace's. Chimera who have an abstract concept or a piece of media as a source will look like they "belong" in or to the source. So if a chimera picked a concept like "nature" as a source, then they'd likely look like a plant person, or a fairy, or a dryad. Or if a chimera picked a popular book as a source, then they may look like a character from that book.
Having access to a source means that they know everything the general public know about that thing, no matter how niche. That chimera with the necklace as a source knows everything the public knows about the necklace, such as how it was stolen 20 years ago and mysteriously reappeared in it's intended place with a note thanking the museum for letting the thief borrow it, and the book chimera knows everything the public knows about the book. The nature chimera, and other abstract concept chimera, are instead rather proficient at something related to their source, with the nature chimera being good at gardening.
It's frowned upon to pick one or a group of living beings as a source due to how unreliable it is. Have you seen how short some species' lifespans is compared to a chimera's? A chimera can live for thousands of years! While a measily human could only live up to a hundred...This doesn't stop anyone from trying to pick the latest boy band from who knows where as a source and immediately regretting it when some member of the band dies from a drug overdose or the band breaks up and everyone forgets about it.