The Pearlescent Charm allows you to pick one of the parent and clone them. There is a 25% chance it will succeed, which is rolled on a 1-4 randomiser! The clone will have the exact same features as the chosen parent: the base, traits and mutations. It will always be the first offspring in a breeding. It can't get anymore trait or mutation from the other parent, even if another item is used!

The Opal Charm allows you to pick a single specific trait or mutation to pass down in a breeding. It is guaranteed to appear on every offsprings. They can stack, which means that you can apply multiple of them on a single breeding to passe down multiple traits or mutations! Chimera would be the exacte same base.

The Topaz Charm allows an offspring to have a randomly rolled fusion based on the first egg group from the parent's fusion. If there are multiple fusions on the parents, you must specify which parents' egg group you want to use. Some pokemons are present in more than 1 group. Dittos can't use this charm as they are the only pokemon in their egg group!

You can learn more about Pokemon egg group here! It will always be the first egg group listed that will be taken into consideration.

The Strange DNA Charm allows one offspring to get a random trait or mutation that none of their parents have. It is rolled randomly among all the traits and mutations possible. It is possible to stack them on a single breeding, and would work this way:
Offspring 1 get a random trait/mutation. If another charm is used, offspring 2 get one as well. And so on. If there are only 2 offsprings but 3 charms are used, the first offspring would get another trait/mutation.