Mew - Pokémon Origins

One of the most elusive Pokemon in the known world, Mew was spotted most recently in Pallet Town. 

Their DNA was used by scientists - headed by Dr Fuji - to create the ultimate Pokemon. The resulting clone, dubbed Mewtwo, would break free and flee to the Cerulean Cave after turning on their creators and destroying the lab. There they would remain until he was captured by Red. 

Red's Chansey - Pokémon Origins

Encountered by Red in the Safari Zone, Chansey ran away from the young trainer while he struggled to decide which was the best way - between rock and bait - to catch her. 

Despite this initial hesitation, he eventually added her to his collection.