Prima

A Mew who is much much much MUCH older than she chooses to appear. She has no legitimate name and just calls herself Prima in the rare instance where she happens to need one.

An underground mafia-esque organization, dubbed "The Syndicate", attempted to hunt her down and capture her - caught totally off-guard by the attack, they managed to rip out a chunk of her hair before she vanished away into the ether. This was enough for them, however. Once Experiment 133 had concluded (an Eevee implanted with chunks of three evolution stones, who later escaped), they used Prima's genetic material to create Experiment 150 (unofficially dubbed "Mewtwo", who later destroyed the lab entirely and escaped).

Prima keeps to herself most of the time, hiding in trees and shadows and just watching people she finds interesting. She knows that pretty much every single Pokemon in this existence has descended from her over time, so she likes to hang out and watch and see how everyone's doing out of a sense of responsibility. When she appears in public, she takes the form of a small cute girl no older than maybe 16. She does this because people are often more inclined to be nicer to small cute girls, and she plays that up a lot. She's also kind of a prankster, though none of her jokes do any harm. Prima is very amused by the looks of confusion her "victims" have once they realize something has changed.

After the Syndicate attack, she has greatly reduced her public presence out of fear. However, once she realizes that there was a being directly based on her, she made it her goal to track him down and watch over him, as she is more directly (even if only on a technicality) his mother.