A chimera is a female, fire-breathing monster with a lion's head, goat's body, and serpent's tail (in Greek Mythology). However, the chimera we're talking about now is simply a hybrid. It is a mixture of two embryos mostly animals but human embryos are also a thing. "Second, chimeras can arise when developing fraternal twins share a blood supply. This happens when the twins (who have different DNA) share a placenta and cells from their blood mix." The ways it's been depicted are the Greek Mythology monster. Below are photos of what a Chimera can be: